A popular design choice for characters in anime is to give them natural hair and/or eye colors that do not occur in real nature.
Red, blue, pink and white are some of the most popular choices for hair and eye color in anime. Often, the colors are chosen to reflect aspects of a character's personality. A character with blue hair is often calm and collected, while a character with red hair often has a wild and fiery personality, a character with red eyes might be evil or mischievous and so on.