I have had mixed results with attempts at multicolor projects. I have tried coloring the focal design first and then added a resist before covering the entire project with the darker background color and then wiping it off the resisted area. I found I needed to touch up the color a bit.
I have colored the design and then, as Chief suggests, carefully started the background color with a small brush.
When using an opaque color Dwight's method works great. Good job on the hawk, Dwight!
Regardless of method a little touch up is usually necessary, at least when I do it.
I like the shotgun butt cover too. Great job!