adjectives - plural nouns: should I add "s" ending to both nouns?

I know I can say

what color of towel do you like?

And the same:

what towel color do you like?

I also know I can say the same about multiple colors:

what colors of towels do you like?

But I'm not sure if I should say:

what towels colors do you like?

or

what towel colors do you like?