You can add it in with the melted marshmallows if you need the whole batch one color, or you can knead it in after it is made, which is usually what I do. Yes, you use the same gel coloring. Good luck!!
Yes, whatever you are using for your BC will work. If you are making a batch all one color, you can put your gel color into the marshmellows AFTER you have melted them, then proceed with the powdered sugar, etc. If you want to make it white, then add your gel colors to different pieces of the MMF, just be sure to wear gloves & grease your hands with crisco.
HTH
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