red-green dichromacy

NOUN
20 LETTERS · STARTS WITH R

red-green dichromacy is a valid 20-letter word worth 33 points in Scrabble and 36 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
R1E1D2-0G2R1E1E1N1D2I1C3H4R1O1M3A1C3Y4
1 + 1 + 2 + 0 + 2 + 1 + 1 + 1 + 1 + 0 + 2 + 1 + 3 + 4 + 1 + 1 + 3 + 1 + 3 + 4 =33 PTS
DOUBLE WORD → 66TRIPLE WORD → 99
MEANING

What does red-green dichromacy mean?