Generally, in BrE, we wouldn't bother with "of" at all and we would use "colour".
What colour clothes do you like boys/girls to wear?
What colour clothes do you think suit boys/girls the best?
What colour clothes do you think look best on boys/girls?
The same applies to all the examples I thought of:
What colour paint do you want me to buy to decorate the kitchen?
What colour books are on that shelf?
What colour socks are you wearing?
What colour dog do you have?
Student or Learner