Erwin I would mix white with yellow at first.
I think when you are not happy with this result you can go on.
give him again deeper shadows with sienna, give him highlights with that mix and the highest lights should be always with. In my opinion.
I used several Andrea fleshtones for base or sometimes fleshreadymix from oils.
Why not.
Darker shadows on the side of the nose and the upper eye.
And more highlights small hightlights I think than you are more satisfied.
Keep posted.
And dont forget at least a little red, or you get an ghost.