I am in the process of making MMF for the first time, as I type. Do you color it the same way you color store bought fondant?
I just use a toothpick to add the color and blend well. This will take time by the way~!~!
the easiest way to color fondant, if you want the whole batch the same color, is to add the gel paste when the marshmallow is melted but before you add the powdered sugar....saves you a ton of kneading.