I don't know if I can provide a proper tutorial. But this is a general idea of how I've been doing the mixed flesh on half orcs. Sort of similar to the giants and trolls... but not.
There's no easy formula or step-by-step process. That's increasingly the case for my process.
I have a pool of washes. Some are stock GW, some are OOP and some are my own concoction. I just sort of pick which first-wash to give a mini as I go. I've usually been doing two washes. Frequently two different colors, but sometimes the same one twice. Some of them get thinned out with a bit of water. Sometimes I will go back and give some additional shading or color only in particular spots with the wash -- maybe for darker, sunken in look to the eyes, or a bit or red around the nose or cheeks, etc. After the washes are done, I'll do some minimal highlighting and that's it!
I tried taking some photos of a few test subjects, but they didn't turn out so great. The proximity of the light an the black background screwed the contrast & color a bit. I'll try a pic in my more neutral-ish photo spot later.