They would have to change color scarves. The robes are black though either with the Hogwarts crest or they sew on their house crest. Whoever said that they didn't mention scarves and ties in the book is wrong.
TBH I think I might be a ravenclaw with slytherin qualities now that I really think about it but did anyone hear about Alan Rickman? I am so so sad right now I loved him a lot.<----- I'm a slytherin with ravenclaw and it is so sad