I bought a rose gold iPhone 6s at the end of December, but I decided I wanted to switch to a different colour. The phone was 0$ when I bought it and I have about 200 on the tab medium. Would there be any way to trade in to get the other colour?
For best value do as Dinh suggests and sell your phone on your own.
Koodo does have a trade in program where they will give you an in store credit that you can use towards a new phone. You will probably have to pay off your tab first. They also won't give you anywhere near what your phone is worth. It is an option though, so you can decide.