How to Make Polka-Dot Soap

First off, you’ll make your dot batch of soap. Scent and colour it however you want, keeping in mind that they are only part of the end result. You should definitely colour them so they’ll contrast with the suspending batch… if you don’t, I’m really not sure why you’re even bothering.
Once the first batch has set up (but not hardened fully, maybe 20ish hours after the pour), roll the soap into little balls. You can do a variety of sizes or make them uniform, but keep in mind the size of the bars you’ll be making. I probably made my balls a bit big for these bars—they kind of take over the bar.

Source: http://www.humblebeeandme.com/how-to-make-polka-dot-soap/