The first part of the sentence starts with ton costume ("your costume", as in a single person). Therefore the second part must also be second person singular: te va and not vous va.
Just to add to Chris' answer, the three forms of you which are possible would be -
Ton costume te va bien
Votre costume vous va bien
Vos costumes vous vont bien
Sign in to submit your answer
Don't have an account yet? Join today
Test your French to the CEFR standard