[mxfh]

Color calibration is a chain, you need to know if your camera is calibrated too, so you need at least standardized targets, finding random objects of known color that cover the whole color space sufficiently is not trival, only then you could use your calibrated camera to measure a displayed target.

But I wouldn't cut corners there and just get a calibration device for about $100 plus a standard color calibration target. Certainly more sensible investment, then the difference between a 2k and 6k rig.