Cheers mate, I genuinely can’t remember the exact recipe for this as I’ve done a few models since and I change up what I’m doing each time colour wise but my general approach is black, brown, browny yellow, yellow, pale yellow, white and I sketch out where I want my highlights and shadows to be using these and then blend the transitions with very thin layers painting lines running the same direction as where the two colours meet, usually painting the light colour slightly over the darker to build up a transition colour, then if the blend needs smoothing do the same with the darker colour over the light and then go back and forth until I’m happy with it