This video tutorial will help you make better decisions when choosing your thread color and zipper for multi-colored fabrics. It's scary to feel confused when you are buying these things and have to commit to sewing with them.
Just play with it. Have fun. Take a scrap of fabric with you when you're shopping for these things, and don't forget to unwind a bit of thread and slide the zipper out of your package!
Place it on your remnant fabric, then pick the best one. By that I mean the color that blends in or camouflages the best.