Yes, mascara on the muzzle is a real no-no. My Mamie has the most jet black/ink black mask I've ever seen, and I've heard ringside comments about how it can't "real." (Just peek inside her flews - those spots are pretty black too, folks!)
Depth of color is something that many lines have lost over the years, and some people fudge their dog's lack of a good mask (which is called ESSENTIAL in the standard) with artificial means.
Chalk is pretty universal dog show stuff -- technically the excuse is that it gets dirt out of the coat or something, so it's a form of shampooing (you're supposed to wipe it all out after) but most people use it to brighten the white.
To me, the essential difference is that the white chalk may enhance color that exists, while adding ink to a poor mask is trying to CONCEAL a fault.
In the grand scheme of things, boxers are showable with a face cloth and some water, assuming they're basically clean to start with. The poodle world has people cheating not only with cans and cans of hair spray but hair extensions as well!