I have been painting tubes and the the blanks for years......I have only painted them white or black. I have this white tint that I ordered after reading a post here, I got a pint, truly a lifetime supply. I am still at work and I can't remember what brand it is, but it is awesome. I can't remember if they didn't have black or I didn't buy any. I will look tomorrow for the brand if you are interested.
I have had great luck for black, which is the bulk of my work, just using testors model paint. I am not saying that I do it right, but I have never had any issues doing it this way:
I mix my epoxy on cardboard.....I put the two parts of the epoxy, so there is a 1/4 inch gap between them........I take the other end of a small plastic cheapo model paint brush and dip two or three drops from a black testors model paint bottle in that gap....mix all thoroughly, and use.
I always let everything dry at least overnight. I used to be worried that the tubes were painted with spray paint, the blanks with acrylic enamel from wally world and testors in the epoxy,truly a "dukes mixture", but I have never had a problem in a couple hundred pens.....
I hope this helps....just my .02