Yes, RUDDIER is a Scrabble word!

Letter values in Scrabble US: R 1, U 1, D 2, D 2, I 1, E 1, R 1.

Is it a valid word?

RUDDIER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

inclined to a healthy reddish color often associated with outdoor life
of a color at the end of the color spectrum (next to orange); resembling the color of blood or cherries or tomatoes or rubies

Also: blood-red, cherry-red, ruby-red.