Bridesmaids usually wear pink bridesmaid dresses. because her dress colour need to have differences with wedding dresses. But it does not necessarily everyone is wearing pink costume. actually, as long as not wearing white of clothes (will and bride of wedding similar) and red of clothes (will and bride of late dress or cheongsam similar) on probably not out what wrong has. I think, light yellow or Lake blue dress.
Cheap prom dresses can be adjusted to be a bridesmaid dress.