Teach Soap

I've been really into bath bombs lately, and I've decided I would really like to make my own for myself, and to give as gifts to friends and family. I've been looking at recipes and such and I noticed that some people use citric acid and some use cream of tartar. Is there a difference in the fizz, or do both work the same? Is one better than the other?
Also, some people use epsom salts and some don't, would anyone suggest using them to not using them?
And lastly, I'll mainly be making these for personal use, so I'm trying to keep the cost down. I would like to use colorant in some of them, and I've read that some people use icing colorant. Is that ok to use? I'm nervous it will stain my skin or my tub!

I prefer citric acid. I don't use icing colorants as they can stain the tub.

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Irena
Closed minds are like faulty parachutes; they refuse to open.

Ok, good to know - that's what I was worried about with the icing colorant. Thank you