They did kind of change that a bit with Grotsnik however. he is described as deciding he needed to be sneakier, so he forsook most of his clothes to let his greenness blend in with the foliage, and used soot to black all the metal on his weapons and equipment.
Although, he is the "sneaky" special character, so typical Blood Axes are probably still less clever.
I like to think the more successful ones blunder onto working unconventional camo schemes without really meaning to. (The kinds that break up outlines, etc.) Also, some of the flamboyant red and orange schemes would work in some kinds of deserts and badlands, or places with reddish brick.
If the Bloodaxes simply resorted to stealing fabric from IG regiments they were fighting or copying it, they would get semi useful camo mostly by accident that way too.