Distinguishing klans

[Tiny]

Aside from colours the details to separate them would be:

Goffs: Horned helmets. Eavy armour.

Deffskulls: Skull motifs. Trinkets. Looted bits. Face Paint.

Snakebites: Primitive weapons. Leather. Topknots. Face paint.

Evil Sunz: Goggles. Fast vehicles. Flame motif.

Bad Moonz: Flashy weapons. Floppy hats.

Blood Axes: Military equipment. Imperial bits. Camouflage.

...

The old fantasy Orc kit had a lot of cool bits for kitbashing GoMo Orks if you can get one. Floppy hats which are reminiscent of the old 2ed Bad Moonz and there are plenty of topknots and primitive bits to make Snakebites. The current Boyz kit makes great Goffs with zero work and the older Boyz kit is strangely still available for variety. There are cool bits in a bunch of other kits to make other clans. Bikers have great Evil Sunz bits. Stormboyz has cool Blood Axe heads and goggles for Evil Sunz. Beast Snaggas make good Snakebites, as do Savage Orruks. A pack of Citadel Skulls gives you enough bits to decorate as many Deffskulls as you could ever want.

 

[Flamekebab]

Lots of good suggestions in here already. I'd be inclined to try to make the different klans a bit distinctive in terms of physique too.
Goffs would be much more heavily muscled, for example.
I tend to think of Deffskulls as sort of ganglier - a bit underfed.
Snakebites would be covered in scars and the odd bandage.
Bad Moonz would be tubbier - lots of beer guts in evidence!

Evil Sunz and Blood Axes don't strike me as being all that physiologically distinct but there's plenty of other ways to distinguish them,

 

[Punktaku]

Ahh…. Maybe that’s why I like the Bad Moons so much…. Although I don’t drink alcohol. Not even beer.

 

[Heart of Storm]

Classic Blood Axes copied the Imperial Guard, even down to such things as using tactics and camouflage, as such they were considered traitorous gits and thoroughly un-orky by other klans

The apex of this were the Bloodaxe Kommandos, who came with webbing, camouflage netting and the like, so in terms of modelling Blood Axes you could take that line and add backpacks, water bottles and other modern military regalia so they seem more "profeshunul'

 

[Punktaku]

@Heart of Storm and those little skully caps.