One color can influence another color.

The human eye (and brain) perceives an object's color not based on its actual color, but on how it compares to the surrounding colors.

The color of Ingrid's eyes, in these photos, are gray. However, if I add a brownish layer to her lenses, but not her irisses, then the eyecolors seem blue, but are still gray.

Check for yourself with the Color Picker in the photo below. Click (or touch) an iris and see the real color in the page's background.