There are a few products that are just insanely useful, and The Mark epoxy is squarely one of them. It's pretty basic: a special epoxy that you can use to mark your metal gear with the pattern and color of your choice so you always know what's what.
With cams, screws and other shiny objects going for $50 and up a pop, The Mark is like a condom for your gear: a prophylactic to prevent that expensive piece from walking away, accidentally or otherwise. Just mix the two ingredients and have about a 30 minute working time to apply to gear. 24 hours later it's bombproof. literally: there may be some chemical to get it off but there's no way mechanical friction or impact will do it.
The Mark comes in red, yellow, green and blue and one package will make about 250 marks. Even better, they thoughtfully include a small and a large application in each package: use the large one to mark your full rack and the small one for pieces you add later. Any way you look at it this is way better than colored tape.