Ringo,
I used the mustard after the blueing was gone to give the gun an older look. I only used it on the steel, not sure what affect it would have on the brass, but basically it just darkens it and gives it some "age". I only did one application of it, but, you might get better results doing it a few times over. To be honest, I know almost zero about it, it was the 1 and only time I've ever attempted it. Also, I did build the box myself.
DD1,
I got the lining for the box at Hobby Lobby. The flash from my camera makes it look bright green, but it's a very dark green color in reality. I didn't have it in this pic but I eventually put a copy of the original colt's loading instructions on the top half of the box.
Thanks for the additional reference CaptainK, I had read that somewhere but wasn't exactly sure.
Nothing like a $30 gun...that's just crazy to me.