Yes, DALTONISM is a Scrabble word!

Letter values in Scrabble US: D 2, A 1, L 1, T 1, O 1, N 1, I 1, S 1, M 3.

Is it a valid word?

DALTONISM is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

dichromacy characterized by a lowered sensitivity to green light resulting in an inability to distinguish green and purplish-red

Also: green-blindness.