When learning how to bake, colouring buttercream/frosting/icing (whatever you want to call it . . . I just call it deliciousness) can be one of those things that seems simple, but a little extra instruction can never hurt.
The most important tip I give anyone starting out, is to invest in the Gel Pastes! The Supermarket run of the mill food colouring dyes will not cut it and you will be left with dull or oddly coloured icing.
The second most important tip I can give you is to add the dye in small amounts until you reach the desired colour/shade.
I have been using Americolor Gels for the last year and love them! Get yourself some of those and you’re set.