My SOP for camoing Icons is to build one of each colour then draw the camo and cut it out and past it into the base colour. If it's a three-tone camo then you do that once for every colour not the base colour.Sometimes I feather it.....sometimes I don't. For winter camo I generally feather it
A technique I use occasionally is to enlarge the Icon 400% then outline the area I want to use for camo. When it's pasted in the Icon then can be reduced 25% and you will be back to normal game size and then apply the palette. Occasionally I use error diffusion but normally it's nearest colour. Sometimes one works better but usually nearest colour is best
The advantage of increasing the size 4x is you can draw a bit more complicated pattern with more control than it would be possible at 1:1

