Very nice detail, Richard.
If this was shot through plexiglass I'd say you did quite well.
I think I prefer Rob's WB Richard,
One other option is to set one of the ACR/LR presets dependent upon the lighting; e.g. Daylight, Shade, Cloudy, etc.
Although they are quite far apart, they may help you decide what looks wrong and go from there with Temperature and/or Tint as seems wise. Also, try the ACR/LR "Automatic" to see what that makes of it compared to your camera's Auto-WB, visible in drop list; "As Shot".
Finding something in the scene which is white (or grey) is another option and using eye dropper, but tricky with this shot, I agree - but as we can see, it can help.
Also, bear in mind that you may be able to do that on another shot (different angle, but same lighting), then transfer the numeric values to the shot you're actually trying to process.
Cheers, Dave
Is the orangutan in a simulated open air enclosure or in natural light? Nice capture.
Thanks gentlemen, you have helped me a lot as my CiC friends always do...
Richard - Plexiglas (Rohm & Haas), Perspex (Imperial Chemicals) and Lucite (Dupont) are trade names of acrylic plastic or more properly known as methyl methacrylate. This material (as do many plastics) tends to yellow when exposed to sunlight, so you might look at adding a bit of blue in post to counter the effect of the yellowing.
I suspect that you are actually shooting through polycarbonate (Lexan is the GE trademark) as it is a more suitable material for this type of enclosure (much harder to break). This material yellows and clouds a bit under UV, so adding a bit of blue and additional sharpening might be required.
I would have used Threshold and Curves and aim for the white part of the beard for the white point.
I did a levels adjustment using the neutral midtones shown and like Izzie used the whites flecks on the chin and the blacks near the face; unfortunately the outcome became electric and would definitely not look like Richard's view. Attachment added to show location of neutral tones. Interestingly enough, I would have thought the neutral areas could be easily chosen by using the grass, surprised that such a small area was included in the search. I used a technique found in Elements tutorial called "Dave's (Cross) Amazing Trick for Finding a Neutra Gray".