I generally don't think too hard about food coloring in marshmallows. Marshmallows are hardly natural these days, so why should I expect their colors to be natural?
I bought, on a whim, a package of "swirled chocolate and vanilla" marshmallows for my family. My husband was happy for an excuse to fire up the ol' fire pit. After roasting beer brats over the open flames, we turned to the marshmallows.
Raw, the marshmallows are a nice cocoa brown, kind of like powdered cocoa. Pretty, soft, pinkish. After a few minutes over the coals, the marshmallows began to take on the classic golden brown of all marshmallows over a campfire. Unfortunately, the nice golden brown on top of the pretty, pinkish undertones combined into a very unappealing shade of baby poop mustard.
We also learned that these cocoa mallows are much tastier toasted only until they begin to warm up, NOT until they crisp up.