Eye styles

Many Anime and manga characters feature large eyes.Osamu Tezuka, who is believed to have been the first to use this technique, was inspired by the exaggerated features of American cartoon characters such as Betty Boop, Mickey Mouse, and Disney's Bambi.Tezuka found that large eyes style allowed his characters to show emotions distinctly. When Tezuka began drawing Ribbon no Kishi, the first manga specifically targeted at young girls, Tezuka further exaggerated the size of the characters' eyes. Indeed, through Ribbon no Kishi, Tezuka set a stylistic template that later shōjo artists tended to follow.

Coloring is added to give eyes, particularly to the cornea, some depth. The depth is accomplished by applying variable color shading. Generally, a mixture of a light shade, the tone color, and a dark shade is used.Cultural anthropologist Matt Thorn argues that Japanese animators and audiences do not perceive such stylized eyes as inherently more or less foreign.

However, not all anime have large eyes. For example, some of the work of  Hayao miyazaki and Toshiro Kawamoto are known for having realistically proportioned eyes, as well as realistic hair colors on their characters. 

References:wikipedia.org/anime