The problem with paint sticks, crayons, acrylic paint, and the like is they will all come off when they come in contact with cleaning solvents.
I find it almost impossible to thoroughly clean my gun without somehow getting cleaning solvent on my painted areas I don't want to come off, and I had to keep touching them up.
I went to hobby shops and craft stores and asked where I could get paint that wouldn't come off with solvent, and after I got the puzzled looks out of the way they finally directed me to a solution of the most durable color paint around.
For a true "permanent" finish, you need to use automotive paint, and by automotive I mean the paint they use to paint your car. It can take some work to get some, but I found by going to a body shop where they paint cars they had the paint I needed. By applying a clear coat on top of that paint, it really helps ensure that your paint won't come off. It can be sort of shiny,but no shinier than a normal acrylic paint.
There are epoxy paints that may be even more durable, but they really aren't suited for this application. Car paint is the best IMO.