Hi, Pat, and welcome!
If you are new to melt-and-pour soapmaking, you may want to check out Soap Queen TV on YouTube (starring Anne-Marie from Bramble Berry):
http://www.youtube.com/user/soapqueentv. Scroll down to the bottom of the episodes on the sidebar and you'll find several on M&P soap. Here's a video specifically about layering:
http://www.youtube.com/user/soapqueentv ... oyh1Bf3GxoFor a black color, I like to use black oxide. A little goes a long way, so don't use too much. I really like BB's liquid oxides for M&P. They're oxides mixed with liquid glycerin so all you have to do is shake it up and add your colorant drop-by-drop. They have a black:
http://www.brambleberry.com/Liquid-Blac ... P3254.aspx. Oxides are stable, so they won't bleed and they stay true to color.
For a zebra striped effect, you could pour alternating layers of white and black. If you want a 50-50 split, I'd figure out how much soap my mold holds (you can fill it with water and then weigh the water to figure out how much a mold holds) and then make half white and half black (or whatever ratio you want). You can make horizontal layers, or if you can find something to put under one side of the mold (I use play-doh) to tilt it at a slight angle, you can get tilted layers, which is a neat effect. (Here's a tutorial about that:
http://www.soapqueen.com/bath-and-body- ... episode-2/)
When doing layers, make sure you pour cool (I pour around 115 degrees) so you don't melt the layer below it, and make sure that the previous layer is firm enough to support the next layer (I test this by gently blowing on it; if I see ripples, it's not ready yet). Also make sure you spritz the previous layer with rubbing alcohol before pouring the next so the layers adhere. Don't wait too long before pours - you want the previous layer to still be warm by set up enough to hold the next layer.
I hope that helps! Have fun!