i don't like NCP thread for a lot of things -- it's completely opaque so you get zero depth to the color, it just looks like paint when epoxy is applied.

with any good thread, the colors don't run, but it goes translucent so it's a good idea to experiment with color choices. a nice trick is to apply one coat of color preserver, so it doesn't completely saturate the thread, then apply the finish, you can get some real depth to the thread color that way.