1. Divide the soap recipe into three and make each color one after the other so that the layers are really even and have a chance to set up. You can premeasure all the ingredients and then start to mix the next batch directly after each layer is in the mold.
2. Once the batch has traced lightly, divide it into three containers and color each one. Then starting with the first container, add the scent...this will usually help to firm it up. Pour it into the mold. Then procede to the next container and scent that one. Very carefully pour that on top of the (hopefully) set layer already in the mold. Do the same with the next layer. This method will usually not have quite the precise level layers but is very nice as well.
I make my layered soap with both methods posted above. I like method 1 the best. I get a more even layer and they usually don't blend together this way.
Must layered soaps like this go through the gel stage? It's my understanding that if it doesn't gel, the layers will fall apart, but I have not yet tried it.
When I made layered soap I started with a clear layer, then added a plain layer the next day, then finally a whipped layer. I didn't gel at all, and it never separated.
edited to say - clear soap made with ethanol, not mp.