Eye color Light and light-mixed eyes (16–12 in Martin scale) Pure light (16–15 in Martin scale) Light-mixed (14–12 in Martin scale) Mixed eyes (11–7 in Martin scale) Mixture of light eyes (blue, gray or green) with brown when light and brown appearance is at the same level. Dark and dark-mixed eyes (6–1 in Martin scale) Amber eyes are of a solid color and have a strong yellowish/golden and russet/coppery tint. This may be due to the deposition of the yellow pigment called lipochrome in the iris (which is also found in green eyes). Amber eyes should not be confused with hazel eyes;
Filling-in the ring (Krauskopf 1967). These stimuli where intermixed with control stimuli, in which the physical colour of the disk was gradually changed to that of the ring. The animals were instructed to signal a colour change, and their responses to control stimuli and to test stimuli were compared in order to determine if monkeys perceive colour filling-in under steady fixation like humans. The authors recorded the activity of surface- and edge-cells (cells whose receptive fields pointed either to the filled-in surface or to the border between the disk and the ring) in the visual cortices V1 and V2 while the