M&P colorants are different than CP colorants. You can use common food dye like at the market for M&P. I wouldn't use it unless it says safe for CP soaping. I haven't seen any discussion on using food dyes in CP soap and I expect there's a reason for that, probably the lye eats up the colors.
I rather like the color that olive oil soap has, usually a milky light green. It's a kind of nice wholesome color. You might like it.
Yeah, if you've got mica, sure. Mix it first in a very small amount of oil. When comes time to use it, take a glop out of your batch and mix the colorant with that. Continue mixing until it is a uniform color, then return the glop to your soap pot and blend it there until everything is uniform in colored. Beware of clumps of mica. Get it mixed really well before you return it to the pot or you'll never get the specks out. Ask me how I know.