colour blindness

NOUN
16 LETTERS · STARTS WITH C

colour blindness is a valid 16-letter word worth 20 points in Scrabble and 27 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
C3O1L1O1U1R1B3L1I1N1D2N1E1S1S1
3 + 1 + 1 + 1 + 1 + 1 + 0 + 3 + 1 + 1 + 1 + 2 + 1 + 1 + 1 + 1 =20 PTS
DOUBLE WORD → 40TRIPLE WORD → 60
MEANING

What does colour blindness mean?