I started (many) years ago trying to paint whites and pupils and didn't do very well. I then went to applying a wash and was reasonabl;y happy with that and have a couple IPMS National awards for figures done that way. In the last few years, however, from hangong with figure guys and learning from them as well as going to figure based shows, I have taken to painting the eyes fully again. Yeah, it's taken some work, but I get pretty good result with a 10/0 brush. It helps if the sculptor has givn you a good canvas, something most 1/35 scale plasticsdon;t have and the older the worse for detail to guide you.
The 20 foot rule works if you're holding a figure at arms length, but in reality, when I examine a figure, I', no more than 18 inches from the figure. Well painted eyes will make a difference here, and certainly, if I'm taking a close up to post on-line, the lack of eye detail is going to be abunmdantly eveident.
T-rex suggests tan for flesh. I have been using Vallejo red beige as a caucasian base. My woodland Indian figures get two parts red beige and one part dark skintone, while a Crow I'm painting right now started with a 1:1 mix of these colors. Varrious combinations of these become the shadows and light flesh becomes the highest light. That color is also the color of the whites of my eyes, with a dot of dark blue oor brown for the iris. I just experimented with a pale blue iris with a pupil done withthe point on a compass.
Here's a recent example in 54mm, just slightly larger than 1/35: