Chroma

Chroma is an ability word first introduced in Eventide. Chroma was featured as rules card 3 of 8 in the Eventide set.

Cards with chroma require a count of the number of specific colored mana symbols on cards.

[edit] Rulings

Different chroma abilities have different effects and check different sets of cards or permanents. Read each card carefully.
Chroma abilities check only mana costs, which are found in a card's upper right corner. They don't count mana symbols that appear in a card's text box.
Chroma abilities count hybrid mana symbols of the appropriate color. For example, a card with mana cost has two red mana symbols in its mana cost.
Many chroma abilities check a set of permanents that includes the one with the chroma ability. For example, Heartlash Cinder's chroma ability includes itself, so it'll get at least +1/+0. Similarly, Primalcrux (a creature with power and toughness each equal to the number of green mana symbols in the mana costs of permanents you control) will be at least 6/6 while it's in play.
Copy effects, such as Spitting Image and Clone, copy a permanent's mana cost (and all the mana symbols therein). A token that's a copy of a permanent will copy that permanent's mana cost, if that permanent has one, and will be counted for chroma abilities.