Currently, I'm using the stuff from Drapa, Candu something. I use the blue for high spots and the yellow for the highlighter. The blue goes on your known "good" piece or surface plate or straight edge, and the yellow goes on the part that will get scraped. The yellow just needs to be a light layer, just enough to give it a faint yellow color to the surface. Any more than that, it blends into the blue and you get green!
For you, the Dikem Prussian blue is probably available easily for you. The first time or two you use it, everything in your shop turns blue. Your hands have it for days on end. Don't matter what you do to clean, there's still resudiul blue left behind.