Heterochromia is when two eyes are of different colors. There can be simply a spot of another hue in one iris, or the eyes can be totally different colors. Curiously enough, the Japanese language refers to this phenomenon as "odd-eye" (オッドアイ, oddo ai).
While Ken Kaneki (from Tokyo Ghoul) is among the most known for his mismatched eyes, there are plenty of other characters on pixiv with the look. Do you recognize any of the others below?