Possible Clues:

• Pigmentary layer of the eye
• Another eye part
• What gives irises their color
• In a certain type of light, each is a bit of a looker
• Sort of light reaches each part of the eye
• Bit of eye makeup?
• The eyes have it, really
• Layer in the eye
• What makes green eyes green
• Eye layer whose name derives from the Latin for 'grape'