Non-cardinal color perception across the retina: easy for orange, hard for burgundy and sky blue

Cardinal color performance (reddish, greenish, bluish, yellowish, black, and white) has been shown to decline in peripheral viewing. What about non-cardinal color performance (e.g., orange, burgundy, and sky blue)? In visual search, performance on non-cardinal colors matched that of the cardinal colors in the (L-M)/(S-(L+M)) (isoluminant) color plane (Experiment 1, n=10, to 30°; Experiment 2, n=3, to 50°). However, performance in the (L-M)/(L+M) and (S-(L+M))/(L+M) color planes was worse for non-cardinal colors, at all eccentricities, even in the fovea. The implications that these results have for the existence of non-cardinal mechanisms in each color plane are discussed.