I went back and forth a few times about how to paint them. I used P3 Cryx Bane Highlight as the main weapon color for my previous Crusties, with the occasional Vallejo Heavy Red detail.
Since the armored Crusties didn't seem to have any skin (shell?) exposed, the gray and dark red seemed like the obvious color choices. But then I was afraid they'd be too close of a match for a recently-painted Ravenstar Silverback mecha, which are Vallejo Gory Red with a few P3 Cryx Bane Highlight details. I second guessed my colors even more after I saw (and fell in love with) the bright orange scheme featured on Gunner's Wargaming. But ultimately I decided to go with the Cryx Bane as a base color and limit the Heavy Red to the weapons and backpacks. It wasn't bad, but needed another color. I ended up using Vallejo Goblin Green on the weapon "fins," some small details on the backpacks, and on the helmet lenses. A quick touch of black Wonder Wash and some base texture completed the figures.
I'm not convinced the green details are bright enough. I might get something brighter (Vallejo Fluorescent Green maybe) and touch them up later. But they are ready for the game table, and match pretty well with my earlier Crusty infantry.
More importantly, this palette should work fine on the Crusty walkers. But I swear... Next time I make a new army - I really need to make sure I stop using the same few base colors. :)