A common trope, especially in video games that feature Elemental Powers, is that every element will have a color associated with it. This way, you know that anything red is related to fire, blue to water, etc.
This can manifest in many ways. Some common ones are enemies being the color of their element, element-resistant armor having that element's color, and elemental spells being color coded in menus.
A few common examples of this trope follow. There are occasions where other colors are used for these elements, and these are by no means the only elements that get color coded.
Wind/Air: Green in most Asian works, yellow otherwise. Sometimes white or grayish, rarely blues or purples. Occationally reds and browns if Autumn themed.
Earth: Yellow, brown, and orange are all common. Green if nature is not separate or if yellow is already taken.
Ice: In settings where water and ice are distinct, water will tend to be a darker blue, while ice tends toward lighter blues, cyan or even white.
Lightning: When Lightning is treated as a separate element (sometimes, it gets lumped with air/weather), it's pretty much always yellow. In the rare cases it isn't yellow, it will be electric blue, purple (thunder clouds), or white. See Yellow Lightning, Blue Lightning.
Wood/Plants/Nature: Usually green, perhaps with other earth tones. If dealing specifically with flowers, it will usually be pink.
Metal/Steel: When treated as a distinct element (rather than a subset of earth), metal is usually a metallic gray, silver, or white (particularly in Wu Xing inspired works).
Light: Usually white or a bright yellow. Pink, if The Power of Love is a major aspect.
Dark: Usually black, though dark purple is also very common. Dark greens if it is also centered on poison.
In Magic Knight Rayearth, fire powers are red, water powers are blue, and wind powers are green. Note that the three main characters were already colour-coded red, blue, and green before getting magic, and then got the associated element.
Used in Ronin Warriors: Red=Fire, Cyan=Water, Green=Light, Blue=Air, Orange=Earth.
Sailor Moon follows almost all of these rules. Sailor Mars has a red fuku, Sailor Mercury has ice and water based powers and a blue fuku (Sailor Neptune has both blue hair and a blue fuku and controls the sea); Sailor Jupiter has lightning, wind, and Green Thumb powers, with a green fuku and pink accents. Sailor Uranus is the Soldier of Flight / Wind and has wind-related powers. Although her main colour is dark blue, the secondary colour of her uniform is gold.
Directly used in Rune Soldier Louie. Although the world doesn't particularly focus on elemental colors, at one point, Louie directly invokes this trope when he has to place five colored orbs in place to represent the five elements. The tricky part is, as this page shows, there's no universally accepted set of colors, so he has some trouble, mostly over if blue represents air or water.
In Keepers of the Elements, each Energy Keeper wears silver, Water Keepers wear blue, Fire Keepers wear red and orange, Earth Keepers wear green, and Air Keepers wear white.
In Clouded Sky, there are temples dedicated to each Pokémon type, and the acolytes of the temples dress in colors that correspond with the type their temple represents (Fire Temple = Red, Water Temple = Blue, etc.).
In The Fifth Element the four stones that are collected represent each element and when opened glow a specific elemental color: red = fire, blue = water, yellow = air and green = earth.
In The Quest of the Unaligned elemental magic is employed in this way, and mages wear the color of the element of magic with which they are aligned. Aeshes, fire mages, wear red; shamais, water mages, wear blue; ruahks, air mages, wear silver; and aretzes, earth mages, wear green. Also shows up in the actual magic of orahs (light aligned) and hosheks (dark aligned), which are gold-white and purple-black versions of the regular elements, respectively. For example, aesh-fire is the same color as regular fire, but orah-fire is pure white and hoshek-fire is dark purple.
Codex Alera has a color associated with the element involved in each of the six types of furycrafting: fire is red, water is blue, earth is green, air is also green, metal is gray, and wood is brown. Each element also has its own symbol, which is on the covers of some editions of the books.
In Tamora Pierce's Circle of Magic series the dedicates of the Living Circle take vows to gods of one of the four elements and then wear habits colored to one of the four elements: red = fire, blue = water, yellow = air and green = earth.
Seen in the theme of the mecha of Rescue Sentai GoGoFive/Power Rangers Lightspeed Rescue: (Using the Rangers names:) Haz Rescue is yellow and a mining truck (Earth), Aero Rescue is green and a helicopter (Air), Pyro Rescue is Red and a fire truck (Fire), Aqua Rescue is blue and a truck with water cannons (Water), Med Rescue is Pink and an ambulance (Life). The Max Solarzord is silver and light blue (Light).
In the former, Mel B represents fire (she wears a red dress and is surrounded by fires in grates); Mel C represents earth (she's meditating on some dry ground that becomes covered in grass); Victoria represents wind (she wears a white catsuit and is standing in a wind tunnel); and Emma represents water (she wears a blue dress and blue shades, and is standing under a fish tank).
In the latter, the elements are swapped round. Victoria represents fire (she wears a red catsuit and is standing on a burning wasteland); Emma represents earth (she wears a green dress and green eyeshadow, and is lying in some grass); Mel B represents wind (she wears a white top and trousers, silver eyeshadow and is in a white room); and Mel C represents water (she wears a blue outfit and blue eyeshadow, and is sitting in some kind of fountain).
Each of the five elements in Exalted is associated with a colour of Jade - the standard Red for Fire and Green for Wood, but a slightly more unusual matchup of White for Earth, Blue for Air, and Black for Water.
When these winds are in their unrefined form, all mixed up, it's Black Magic, while when they are refined to their maximum potential, they become High Magic (manifesting as either silver or as a rainbow).
Magic: The Gathering is all about this; the entire resource system is based around mana coming in five different colors, each associated with a different land feature and set of elements: white for plains, law, order, and (the literal sense of) light; blue for islands, water, wind, and intellect; black for swamps, death, (again, the literal sense of) darkness, and ambition; red for mountains, chaos, fire, and lightning; and green for forests, life, growth, and wildness. There are also colorless artifacts (and occasionally other things) with more generic abilities.
The six elements in The Dark Eye are coded (at least by human standards) mostly this way with a few exceptions: fire is red, wind is yellow or colorless, ice is purple or light blue, water is blue, rock/stone is orange and humus(earth and plants as well as all living things) is represented by earthen colors, but usually by green.
This trope is one of the main aspects in LEGO's BIONICLE and its related lines, Slizers, Robo Riders, and, to an extent, Hero Factory. Especially in Bionicle, there are confusingly many combinations and exceptions, but generally, red (sometimes with yellow or black) means fire, blue (sometimes with added white) is water, green is air or jungle, white (may be part-blue or gray) is ice, black (sometimes with gray, red, orange, tan, or purple) is earth or rock, brown or yellow (at times with gray, orange, or tan) is stone or sand. Some elements can change their colors, and numerous colorful characters don't even have elements, making the whole thing even more difficult. Then, there are secondary elements that use the pre-established colors of main elements as either their main or secondary colors! And this is just Bionicle!
In Tales of Symphonia, the color of the magic circle that appears when an ally or enemy is casting a spell changes depending on the element. Red for fire, blue for water, green for wind, bright blue for ice, brown-orange for earth, black for dark, white for light, and purple for lightning.
In Fire Emblem, the color of a spellbook is determined by what element it is. Bright yellow for light, black for dark, red/orange for fire, green for wind (though the more ice-ish are blue), and yellow for thunder. The last three are lumped as "anima" in the GBA games, making them quite multicolor compared to light and dark.
In Mega Man Zero and Mega Man ZX, Fire is associated with Red, Water/Ice is associated with Blue, Electric/Wind is associated with both Green and Yellow, and Non-elemental is associated with Purple.
In Lords Of Magic, each element is associated with a faith, which fills the role of races or civilizations in other games. Each faith's units have color schemes that fit the above trends.
The Legend of Dragoon color-coded all the elements thusly: Fire is red, Water is light blue, Wind is green, Earth is gold, Darkness is indigo, Light is yellow (though the Dragoon is White-Silver), and Thunder is violet.
ZanZarah: The Hidden Portal's Table of Effectiveness lists Nature as green, Stone as grayish brown, Water as blue, Fire as orange, Air as white, Light as yellow, Darkness as purple, Chaos as burgundy red, Ice as whitish-bluish-cyanish-something, Energy as violet/bright purple, Psi as cyan, and Metal as steely gray.
Pokémon generally follows a skin color scheme based on the element of the Pokémon: Fire pokémon having lots of red or orange, Water pokémon having lots of blue and so on...at least, in the first couple of games. The later generations also featured color-coded icons for each type, though many of them have two colors (e.g., the Dragon-type is half-red, half-blue). Later games updated the icons to all be single-colored (so Dragon is now royal blue).
In Secret of Mana, all the spells of a given school, which are element-based, have the same color scheme.
World of Warcraft has Fire as red/orange, Ice/water as blue, Holy as yellow, Shadow as black/purple, Nature as green and Arcane as pink/purple.
Chrono Cross skips naming the elements directly and just uses colors for elemental affinities. Red is fire and heat, Blue is water and ice, Green is air and nature, Yellow is earth and electricity, Black is shadow and gravity, and White is light and celestial bodies.
Skies of Arcadia does something similar, although the colors are different: Green is nature, Purple is ice, Blue is both wind and water, Red is fire, Yellow is electricity, and Silver is both life and death. Each of these color-elements is governed by an appropriately colored Weird Moon.
Played straight in Distorted Travesty with Fire, Earth, Wind, and Water for elemental techniques. (Unfortunately, the brown looks too much like red).
Onimusha in all its four (and more) games has shown: Lightning (navy), Fire (fire red), Wind (green), Ice (powder blue), Earth (orange), Light (gold) and Air (sky blue). The Dark element appears, but as an alternative name for Lightning.
Bomberman 64: The Second Attack has different elements for different bomb upgrades you can get. You start out with Fire, the traditional bomb with a cross shaped explosion, and can upgrade to Ice, Wind, Lightning, Earth, which is more of a magma bomb, Light, and Dark. Each enemy takes damage differently from each bomb; for example, metallic enemies aren't harmed at all by the Light bomb, aquatic enemies are fine with Ice, etc.
In the Dept Heaven games, we have Fire (red), Ice (light blue), Lightning (yellow), Darkness (purple), and Light (green; sometimes referred to as Sanctity instead).
In Final Fantasy XIII, light blue = ice, red = fire, yellow = thunder/lightning, medium blue = water, orange-brown = earth. Also has reddish pink = physical attacks and purple = non-elemental magic.
World 6-F1 (RGB Factory) in Super Mario Fusion Revival: This fortress level takes place in a high-tech factory with three distinct areas: a red area (lava and fire), a green area (overrun with plant life), and a blue area (a swimming area). This is a key hunt level with a central hub that leads to a boss fight with Dobkeratops of R-Type fame.
Magicka color-codes all ten elements thusly: blue for water, green for life, gold for shield, pale blue for cold, purple for lightning, red for arkane, brown for earth, and orange for fire. If you haven't memorized all of them by position yet, chances are you'll be reading the key based on the colors rather than the pictures.
Borderlands uses orange for fire, blue for shock (lightning), green for acid, and yellow for explosives. The sequel adds a fifth element, "slag", which has properties similar to "ice" in most games. It's represented by purple.
Gauntlet:Legends and Gauntlet: Dark Legacy had the following scheme for shot-power and magic potion power-ups: Red was Fire, Blue was Lightning, Yellow was Light, and Green was acid. Knowing which element your shot power was could tell if it boosted attack power or didn't against a boss.
Golden Sun makes it easy to identify Adepts, as they'll usually wear colors associated with their element, or even have Elemental Hair or eye colors. Mars (Fire) tends toward reds and oranges. Mercury (Water/Ice) is inevitably blue, usually cyan. Venus (Earth and Plants) can be gold, green, and/or brown. Jupiter (Wind/Electric/Telepathy) tends to be green or light purple.
Homestuck has all players given a class and element, in the style of Hero of Element. There are many different classes, each of which can interpret elements in different ways and titles aren't immediately intuitive. The three thus far shown Heroes of Light all have drastically different abilities. However, elements typically can be loosely defined.
Breath (Wind) is associated with blue, ranging from a pale sky blue to darker navy.
Light (Luck) is associated with yellow and orange.
The Questport Chronicles has the elemental essences: Fire (red), Water (blue), Air (light green), Earth (brown), and Aether (black).
In Avatar: The Last Airbender , clothing is color-coded by nation and the wielders of Elemental Powers therein. Air Nomads wear oranges and yellows, Earth Kingdom citizens wear greens and browns, Fire Nation citizens wear reds and blacks, and members of the Southern and Northern Water Tribes wear blues, whites, and purples. This also extends to the colors of Team Avatar's members, since they're essentially an in-universe Five-Token Band. There are some exceptions; for instance, The Order of the White Lotus consists of citizens from all the different Nations, and they have one type of uniform which, while dark-blue like some Water Tribe clothing, is distinct from any one Nation's style shown in the series and Azula's famous blue fire as opposed to the traditional red-orange that all other character use.