tri·tan·o·pi·a 
(trī′tə-nōpē-ə)
(trī′tə-nōpē-ə)n.
A visual defect characterized by the inability to discern blue and yellow.
[Greek tritos, third; see trei- in the Appendix of Indo-European roots + Greek anōpiā, blindness (an-, not; see A-1 + -ōpiā, -opia), so called because blue is considered the third of the primary colors.]