The gold is as easy as is gets. Benchwood Casey Gold Stick Engraving Enhancer. Costs around $7, but I had a hard time finding anyone with it in stock. It is like a big crayon.
It takes a little bit of experimenting to do it so it looks good, but almost anyone can get the hang of it. (Worst case rub some Hoppe’s on it and (sometimes) a quick swipe or two of a toothbrush and start over.)
It lasts quite a while if you don’t rub too hard when you clean your gun. I use gun scrubber and spray it right on, doesn’t seem to bother it much.
If you do a good job and take care when you clean, it will last 1 or 2 months.