Trying to avoid the random viewport crashes I've been changing my normal settings.
However, when I was switching from CPU only to GPU only on the same viewport I noticed that the colours are vastly different between the two.
In fact if you render the viewport with both CPU and GPU checked you get a "fight" on the screen between the two colour ways in the render.
See screenshots for all three issues above.
Blender 2.79b
macOS 10.13.6
dGPU Radeon Pro 560
(no eGPUs)