At a craft supply store I found "Nuvo Chrystal Drops" by Tonic Studios.
This is a 1oz (or thereabouts) squeeze bottle of colored gel that can be applied to paper to make raised colored dots, bumps and other greebles.
I have been experimenting with it, the small drops make excellent rivets for medium to large scale WWI tanks, and with a stencil it might be possible to make tread plates, or raised tire treads.
I looked on internet and found Nuvo Embellishment Mousse, which seems to be more or less the same stuff but in a jar, rather than a squeeze bottle. The drops come in many colors including black, white, grey, and several shades of green.
https://www.tonic-studios.com/collec...tal-drops/nuvo