I call this technique the "pour and scrape" because that's exactly what you will be doing. Pouring a little, then scraping any excess overpour. GoPlanetEarth.com sells a handy little molding tool that allows you to easily scrape away any soap that overflows from the raised area you are pouring.
The secret to your success is this molding tool AND starting your colored pours in the deepest areas first. In looking at the lighthouse soap, you would start your first color pour with the crashing waves. The waves are the deepest area of this design. Next you would move on to the house. The roof is deeper than the white portion of the house, therefore, you pour the roof first. You continue in this manner until you have filled all areas of the raised design.
Allow each poured area to set up and harden a bit. Then, using your molding tool, gently scrape away any overpour. Once you've scraped and defined the poured area, begin your next pour. Again, allow the poured soap to harden a bit before removing any overpour. It's a tedious process and certainly not a technique used for mass productions. Defined color pours appease the artistic side of the soaper. The finished soap becomes a work of art and likely the reason they can retail for $7-$8 per bar.
Here are a few added pointers for success.
1) It's a good idea to have your soap colored before you start. I save all my soap scraps from other soaping projects and the "pour and scrape" technique is a great way to use them up. I also keep a number of glass measuring cups on hand. This allows me to put different colors in each cup for melting and helps speed the process. A quick zap in the microwave easily melts the soap to a pouring consistency.
2) Be careful you don't overheat the soap base. Pouring the soap at too high of a temp will cause the soap to puncture and bleed into you previous pour.
3) Spritz each poured soap layer with a little rubbing alcohol before pouring the next layer. It will help the next layer to adhere to each other.
4) Allow the soap to set up completely before trying to remove. When you have mulitple colored layers, especially in very small area, you need to be gentle when removing the finished soap from the mold. Otherwise, you could find some of your colored layers don't release and end up stuck in the mold. Not a good thing!
So there you have it.... creating soap with defined colored areas.