red-green colour blindness

NOUN
26 LETTERS · STARTS WITH R

red-green colour blindness is a valid 26-letter word worth 30 points in Scrabble and 39 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
R1E1D2-0G2R1E1E1N1C3O1L1O1U1R1B3L1I1N1D2N1E1S1S1
1 + 1 + 2 + 0 + 2 + 1 + 1 + 1 + 1 + 0 + 3 + 1 + 1 + 1 + 1 + 1 + 0 + 3 + 1 + 1 + 1 + 2 + 1 + 1 + 1 + 1 =30 PTS
DOUBLE WORD → 60TRIPLE WORD → 90
MEANING

What does red-green colour blindness mean?