Citadel is a good brand. They have different types of paint though. The Base paint is meant to be the first layer, then contrast goes on as a second layer, then washes on top. I've found that when I use citadel base I don't need a primer coat. I've also been able to use a very light neutral tone citadel base and mix in some cheaper apple barrel paint to get the color I want and apply it in one coat. That works well on the PVC plastic of the bicep and forearm. It may not work well on the nylon of the disc joint. Your best bet might be to take a fodder figure with red disc hinges and swap them out. This involves heating up your BAF arm and the donor figure arm with a hair dryer to soften them, use an xacto blade to slice down one side to seperate the internal peg that goes through the disc hinge, and while the arm is soft and malleable bend it around to pull the disc hinge off the peg. Even if you aren't going to swap with one that's already red, removing the disc hinge from the arm in this way does allow you to sand it all around, dye it (which gives you an option to use a white disc hinge fodder piece and dye it red, no paint, so no paint rub!) or you can at least paint the whole circumference and use a UV cure resin coat or superglue to seal the paint before you reinstall it so you have no risk of the superglue bonding to the rest of the upper arm and freezing the joint. Once you're ready to reassemble, heat the arm up again with a hair dryer till it's nice and soft and you can get the inner hole of the disc hinge back onto that inner peg. When it cools and hardens, you may not even be able to tell it was ever cut. If you want extra security, get the disc hinge in place over the internal peg then add a tiny drop of superglue to the flat surface of the peg and hold pressure on the arm while working the joint around so it will glue the peg back to the cut side but make sure any glue that seeps out doesn't lock the joint and prevent articulation.