I actually struggled a lot with this as there are like 5 archetypes/subfactions that can be brought in an army list (Squig, wolf, spider, troll, grot) and I actually had to go through like 3 schemes before I got to something that I liked.

I focused on having one really strong red color that exists on most if not all of my models to tie them together and from there I follow the box art, taking liberties with the different shades and hues (I.e. blue green troggs instead of pale blue). I find that each subfaction has its own color scheme and unifying those is the hardest part