There are stereotyped object colors that are highly prevalent in fiction, but do not reflect Real Life color variations. They have become embedded in popular consciousness through sheer repetition, and sometimes Editorial Synesthesia, to the point that exceptions just seem odd.
In Real Life, grapes can be blackened dark blue, yellow-green, red violet, and red, but in fiction, they're purple because purple is the color grapes are associated with (as well as being the color of Cabernet Sauvignon, the stereotypical red wine people always imagine). Green might be used, but it would give the impression the grapes are underripe.
Blue or Light Blue Water
In Real Life, water comes in a wide range of colors, including clear, turquoise, cyan, light blue, blue-green, dark green, dark blue, and the stereotypical bright shade of blue.note
Not so much in fiction, where water is usually a bright shade of blue. Water Is Blue because it's easier to animate than a transparent liquid and because large amounts of water appear blue due to the way it diffuses light. This subtrope, which is highly prevalent in fiction, does not reflect how Real Life water is entirely accurately.
Back when it had its planetary status, Pluto was often depicted as blue. This most likely had to do with the cold nature of the stellar body, but was probably helped by being near the truly blue Uranus and Neptune. It wasn't until photos came back from New Horizons that Pluto was revealed to be a lovely shade of peach (much closer to the color of Mickey Mouses dog of the same name). People on social media invoked this trope by (often jokingly) insisting the dwarf planet was blue.
Green or Yellow Green Acid
It even has a shade named after it despite the fact that green acidic substances are rare, and no strong or commonly used acids are green (in fact they tend to be transparent as they are usually most active in when in watery solution).
Green or Yellow Green Grass
In fiction, grass is usually green or yellow green because green or yellow green grass is iconic and easily recognizable. What people are usually thinking of is "Kentucky bluegrass", which became a status symbol for front lawns of suburban homes in the 20th century.
In Real Life, golden yellow, light brown, and sandy yellow, as well as the stereotypical green and yellow green, are common colors for grass.
Green or Yellow Green Radioactive Nuclear Waste
Green and yellow green are the colors associated with nuclear waste, radiation, and anything nuclear even though this is seldom the case in Real Life. Cherenkov radiation in the pools of nuclear reactors is blue◊, radioactive cesium chloride fluoresces faintly blue, and hot radioactives are orange◊.
The association with the colors green and yellow green and nuclear waste comes from peoples' experience with radium painted watch dials, which glow pale green. Watch dials haven't contained radium for decades. Currently they use a similar sort of paint but no radium; it absorbs light when placed in light and then glows for a while in the dark.
In Real Life, the sun is white or yellowish white, but in fiction its yellowness is played up because yellow is the color associated with the sun. Part of the confusion is likely because the sun is classified as a yellow dwarf star. That said, stars have very weak colors in general. "Red" dwarf stars, for example. are more of a dark orange.
Yellow or Gold Stars
In Real Life stars can be one of several colors (see below), but the stars the naked eye can see in the night sky are white. In fiction, stars in the sky—especially those drawn as large, five-pointed "sticker" stars—are usually yellow to contrast the night sky's dark blue.
Star-shaped stickers and badges are virtually always gold in fiction because they're given out in a congratulatory manner—in other words, they're a proxy for a gold medal. Needless to say, in Real Life you can get star stickers and badges in pretty much any color, though gold is still the most popular.
Throughout the universe, stars can be blue, blue-white, white, cream, yellow, orange, or red; this depends on their temperature, with hotter stars being bluer. This can be confusing to people who associate red with hot and blue with cold!
An interesting inversion of this are neutron stars, which in many illustrated astronomy books are shown as being red. In reality, due to their very nature, they are invariably white.
Yellow or Orange Cheese
Cheese comes in many colors, including yellow, orange, yellow-orange, light yellow, red, white, and even blue, but in cartoons, it's hard to find any examples where cheese hasn't been depicted cheddar yellow-orange or orange.
Bright orange cheeses, especially cheddar, are usually that color because it's been colored.
Almost all carrots in fiction are bright orange because an orange carrot is iconic and easily recognizable and orange is the most common color seen in Reallife Western carrots. note
This association with the color orange and carrots is Newer Than They Think, as the common orange carrots in the Western world were only bred that color a few centuries ago by farmers in the Netherlands, out of patriotic reverence for the House of Orange-Nassau. Before this, most carrots in the West were actually purple. No, really, carrots used to be purple. And carrots come in other colors, like yellow, red, purplish red, and white◊.
Most apples in fiction are bright red because a red apple is iconic and easily recognizable.
In Real Life, apples come in a wide range of colors, including red, orange, yellow, and green, and can be more than one of those colors as well.
A common exception would be "sour apple" or candies that are apple flavored, which are often green, especially to distinguish other flavors, such as strawberry or cherry, that are almost always red.
Red Fire Hydrants
In Real Life, they come in a wide range of colors, including yellow (both light and golden shades), pink, white, dark green, orange, dull shades of red, and the stereotypical bright shade of red, and can even have two or more colors on them (like San Franciscos blue and white fire hydrants).
Not so much in fiction, where almost all fire hydrants are bright red. Fictional fire hydrants are usually red because a red hydrant is iconic and easily recognizable. This subtrope, which is highly prevalent in fiction, does not reflect how Real Life fire hydrants are.
Brown or Green Polluted Water
Water intended to look polluted is colored either olive green, yellow-green, or brown rather than blue or clear.
Same concept is also commonly applied to swamp water, "blackwater" in real life can look brown, tan, greenish, or pitch black.
In fiction, coconuts will usually be brown like a mature coconut.
In Real Life, coconuts are either green or yellow at their immature state, turning brown as they ripen.
An exception to this would be coconut drinks, which are often shown as the green young coconut.
Sand-Colored Pyramids and Sphinx
During Ancient Egypt, pyramids were originally covered in limestone and gold, making them white with a gold tip. But over the years, the gold was stolen and the limestone was taken for the constructions of other buildings in Cairo, thus giving the pyramids the sand-yellow color they have today.
The Sphinx was also originally brightly-colored; traces of pigment suggests it had a red body, a yellow and blue headdress, blue eye markings, and a blue beard (now broken off). Its now sandy coloring may have been a result of burial and erosion over the millennia.
However in fiction, both are usually depicted as sand-colored regardless of time period.
The skin colour of white people is nearly always depicted as pink, and we're told it's pink, but in reality its a much more subtle selection of light browns, translucency, red beneath the skin, with some blue. It's also often depicted as the stereotypical "Celtic" skin tone: very pale pink, turning bright pink or red when sunburned or after strenuous exercise, when many people of European descent are at least a little darker. Caucasians with darker shades might just be colored brown out of sheer laziness (see Phenotype Stereotype).
Black people in fiction are always milk-chocolate brown, or even mahogany red. In real life, people who self-identify as 'black' can vary in color from pale (beige) to very dark (seal-brown) but this range is rarely depicted. Aboriginals of Australia and East Indians have skin tones with a similar shade variety but they are also exemplified by a middle shade of brown or reddish Brown. Giving a character a top square "Starbucks" complexion, meanwhile, may make their ethicity ambiguous (light black, dark white, or beige Asian).
East Asians run the color spectrum, from very light-skinned Manchu-Tungus peoples of the far north to dark-orange or light-to-medium-brown Austronesians (Indonesians, Filipinos, etc.) of the south. But most Westerners expect to see the kind of maize-yellow (like The Simpsons) complexion that no human being would have in real life unless suffering from jaundice.