This is a visual shorthand trope that makes gems identifiable on sight, often reducing gems to Palette Swaps of each other. In Real Life, there are many features that differentiate minerals, gemstones, precious metals, and organic gems from each other: hardness, smoothness, clarity, a range of possible colors, and location found. But the only feature the audience can directly see for themselves, and that most people outside of geologists are readily familiar with, is color. Therefore, gems in fiction will often be identified solely by color, with a standard set of gem-color associations dictating the types of gems. The gems may be identical aside from the differences in color.
Generally, the code is as follows:
Amber: Yellow or orange
Topaz: Orange or yellow
Diamond: White or clear, possibly with light blue or yellow mixed in
Gold: Yellow, orange, or tannish
Silver: Medium to light gray, possibly with a little blue mixed in
Played with somewhat in The Stormlight Archive, where there are ten gemstones used in Soulcasting; each gemstone can transmute a certain element, and the association is based mainly on the commonality of colour between them. In order, with colours and elements listed, the gemstones are: Sapphire, blue, any clear gas. Smokestone, black, any opaque gas. Ruby, red, fire. Diamond, white, crystal. Emerald, green, plant matter. Garnet, rusty red, blood. Zircon, yellow, oil. Amethyst, purple, metal. Topaz, brown, stone. Heliodor, golden, flesh.
Aoki Lapis is named for the Lapis Lazuli Gemstone and has a color scheme of blue and purple.
[[folder: Tabletop Games]]
Yu-Gi-Oh! has the Gem-Knight cards (a Homage to the Elemental Hero archetype and the above-mentioned Crystal Beasts) which are named for and usually colored after a Gemstone (The exception is Gem-Knight Lazuli and maybe Gem-Knight Sardonyx) Their leader Gem-Knight Master Diamond has white armor and an All Your Colors CombinedRainbow Motif sword and background.
Zig-zagged with The Legend of Kyrandia: Book One. In addition to having all the common gemstones and colors, the game includes a variety of other jewels, as one puzzle revolves around birthstones. One of the first items the player can pick up is a bright red garnet, and the first green-colored stone the player is likely to see is a peridot. The rubies and emeralds are trickier to acquire.
Skyward Sword brought this back with the Emerald Tablet for the Forest, Ruby Tablet for the Volcano and for the first time Amber Tablet representing Yellow for the Desert.
Neverwinter Nights 1 has gemstones which all follow the stock-standard colors mentioned in the description.
Mine Craft: Emeralds are a conventional green, Diamonds are light blue.
In Last Train to Blue Moon Canyon, the gemstones Nancy must find to operate a device not only look exactly as this trope predicts, but exactly like the pictures of their type in a book Nancy acquires.
Pokιmon: The original Generation I games were Red, Green, and Blue. For Generation III, which was essentially a continuity reboot (couldn't link back to Gen I/II games, and included updated Retcon remakes of Gen I,) started with Ruby, Sapphire, and Emerald.
Gen IV's Diamond Version was a pale blue.
One dungeon in Shining the Holy Ark has the player collecting different coloured gem stones to use in a Soup Cans puzzle. The only way to figure out what gem went where was were was if you knew what the stock colours of the gems where.
Sonic the Hedgehog: Both played straight and averted. The Master Emerald which stands alone, is green. The Chaos Emeralds are a set of seven, only one is green and the others are differentiated by color. Given the Real Life example below they should probably be called Chaos Beryl instead.
Final Fantasy IX has the twelve birthstone jewels as equipped accessories, with their menu icons appropriately colored. Dissidia: Final Fantasy includes the same items as trade accessories, minus the Garnet and Amethyst.
Paper Mario: The Thousand-Year Door: The crystal stars which must be collected throughout this game are coloured as such. The diamond, emerald, ruby, sapphire and garnet stars are white, green, red, blue and reddish-orange, respectively. Another star is palette swapped for gold and referred to as the "gold star", despite it being obvious that the star is a crystal not a metal. Perhaps a slight inversion as the last star is an iridescent white, yet it is the "crystal star" not diamond.
In Diablo 2, you could find the six gems that are explained in their description, each with the colour that it's said in the description. What's more, adding them to Socketed Equipment gives it a glow of the colour of the gem, and some of them (to be precise, ruby, sapphire, topaz and emerald) are associated with elements, adding damage of that element in weapons and resistance to the element in shields (ruby is fire, sapphire is cold, topaz is lightning and emerald is poison). The other two (diamond and amethyst) aren't, though.* In Runescape, there are blue sapphires, red rubies, green emeralds, white diamonds, and black onyx. But there are also quest-related gems that are different in color (blood diamond is red, smoke diamond is gray, shadow diamond is black, ice diamond is light gray). Lastly, jade, opal and diamond are in ridiculously similar color. You can have a reference here.
Nethack plays this one dead straight, with a few exceptions - there's two possibilities each for turquoise and aquamarine (green or blue), and fluorite is randomly assigned either green, blue, white or violet. All gems are just "< colour > gem" until identified, so an unidentified "red gem" can't turn out to be sapphire, which is a blue gem.
Partly averted in Dwarf Fortress, which has diamonds of five colours as well as clear, and also blue, clear and pink garnets in addition to red, and so on and so forth. It assigns the standard colors to emerald, ruby, sapphire, amethyst, topaz and quite a few others, though.
[[folder: Web Comics]]
The 8 Disaster Stones in Cucumber Quest have each a color, symbol and element.
[[folder: Web Games]]
Ginormo Sword has gems as enemy drops which are used to apply elemental power to your weapons and armor:
Birthstones are most popular/valuable/expensive in specific colors, and are the Trope Codifier
January Birthstone Garnet - Deep Red
February Birthstone Amethyst - Purple
March Birthstone Aquamarine - Light Blue
April Birthstone Diamond - White or Clear
May Birthstone Emerald - Green
June Birthstone Pearl - White or Cream
July Birthstone Ruby - Red
August Birthstone Peridot - Yellow-Green
September Birthstone Sapphire - Blue
October Birthstone Opal - White or Pink
November Birtstone Topaz - Orange
December Birthstone Turquoise - Blue-Green
The range of colors for some minerals is limited and the trope usually reflects that. For example
Rubies and sapphires are actually the same material. The only difference is that rubies are the red kind, and Sapphires are other colors including but not exclusively the blue kind. The only other color besides red that gets a specific name are orangish ones calls padparadscha.
Similarly emeralds are specifically the green variety of Beryl. Aquamarine is blue beryl.
Aveted however by Real Life Diamonds. With perfect structure and no impurities they are totally transparent and colorless. However with impurities they can be in all kinds of colors, including red, orange, yellow, green, cyan, blue, indigo, violet, magneta. What's more, even gray and black diamond exists[[hottip:*:by reaching a certain degree of saturation]], leaving the only missing color white.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
Is that what you meant to do?
You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.