I used the following recipe to make both my red and blue marshmallow fondant. This recipe uses colored candy melts to start with the base color, then you add your gel coloring. Using this method, you need as much coloring and the flavor is much better.
I used the following recipe to just make the white fondant, though I didn't like this as much as the recipe above. The texture wasn't as easy to work with and the flavor wasn't as nice as the fondant with the candy melts. I believe in the future, I will make the recipe above and just use white candy melts for white fondant. Someone else may have better luck with the recipe below. This was my first time working with fondant, so perhaps my lack of experiece affected how I made this one.