Anne-Marie has some tutorials on how to do ones with multiple colors. Really all your doing is filling the details of the mold first, letting that harden and then filling the rest of the mold.
Here's some of her tutorials:
http://www.soapqueen.com/bath-and-body- ... -tutorial/http://www.soapqueen.com/bath-and-body- ... bet-soaps/http://www.soapqueen.com/bath-and-body- ... -soap-kit/To get the a very vivid color in MP, it's so much easier to use transparent soap and get it a little bit darker than the color you're going for and then add just a tiny bit of melted opaque MP soap to make it not transparent anymore.