Since you're specifically asking for an "RGB" histogram: I'm afraid, this is not possible.
However, If you're fine with an "intensity" histogram without differentiating for RGB, then maybe you'll want to take a look at this.
When you review your image after capture you can view a RGB Histogram.
Is it possible to view this RGB Live Histogram by assigning it to a C1, C2 etc button, which you can press to view it before you take the shot, rather than after the capture.
I am seriously changing my equipment to the Sony range.
With my current eyesight I need the most consistent and accurate Eye AF for non static people shots.
The 24 or 42 meg sensors are not an issue, both would be fine.
Any advice regarding the A9 vs A7R111 would be most appreciated regarding the Eye AF.