I use glossy and matt black camera paint (CF3-F and CF6-F), and they both work very well. First I tried them on some piece of aluminium to check the effect. For engraved numbers, I use white fill-in paint. This one needed some trial and error before I was happy with the result: you need to rub in the paint and wipe off the excess, which to me turned out to be not as easy as it seems. But after some practice it works well too.