Video would help; if you've left any 'smart settings' on in the camera, it's possible that the changing light from the game reflecting off your face could be prompting the camera to adjust some parameter; white balance, gain, exposure, aperture, brightness, contrast, even the focus could mess with things.
Would need to see a video of it happening, but that'd be my first guess. Turn EVERYTHING ABOUT THE CAMERA to manual operation mode.
Did you note the 'before' and 'after' RGB values from your chromascreen sampled color? What are you using as far as similarity/blend/spill?
