In Real Life, almost every gemstone has a range of colors, depending on the crystal formation, and/or impuries in the gemstone. Diamonds deserve special mention here - with perfect structure and no impurities they are totally transparent (has no color), but in practical they can be in all kinds of color, 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. And human have made a complex scale for every gem to categorise its color, which could ruin its value, or make it skyrocket. In fiction, however, no, you won't see diamonds in all kinds of color. Not even all other gemstones - they won't get their full range of color at all, but rather, in one specific stereotype color that's associated with it. And perhaps to add bonus to it, each gemstone is associated with one colour, which in total forms a Chromatic Arrangement, like so:
- Rubies are red;
- Topaz are yellow;
- Emeralds are green;
- Sapphires are blue;
- Amethysts are purple;
- And finally, diamonds are white[[hottip:*:which we couldn't show in white text, but whatever]];
- In the DC Universe, Eclipso's powers are focused through/caused by a black diamond.
- Averted with the "Heart Of The Ocean", a fictional blue Diamond set in a necklace that was a key object in the film Titanic.
- 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.
- Rifts usually subverts this. In using gems as Power Crystals for Techno-Wizard devices, gem types of alternate colors are often mentioned and actually have their own magic separate from the standard color.
- 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's it's not ended yet: 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.
- The Legend of Zelda
- Averted in Sonic the Hedgehog, The Seven Chaos Emeralds come in different colors which tended to change from game to game until it was standardized in Sonic Adventure. Since then, they are consistently Red, Blue, Green, Yellow, Purple, Cyan, and White. There are also several other jewels in the series in different colors, all refered to as Emeralds.
- 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 colours to emerald, ruby, sapphire, amethyst, topaz and quite a few others, though.
- 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.
- Bubble Bobble has gemstones in five of the spectrum colours (its sequel, Rainbow Islands, adds the missing two - red and green), but they're all treated as diamonds (probably because they conform to the stereotypical 2-D diamond shape - the point-down pentagon, which is surely also a trope).
- Minecraft emeralds are a conventional green, but the diamonds are an unconventional cyan.
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