You could have a camera capable of taking RGB pictures, but you would still have to find out what to think of as true color for calibration... And of course, it would have many disadvantages... The most important would be that the channels of the imaging would not utilize the full grayscale range; one would have to maintain either the absolute intensity of all channels or the relative, so you would loose detail compared to grayscale optimized images. This reduction in grayscale resolution is not easy to undo by post processing the image... This has been discussed on several earlier threads.

Some people may think that sticking something like a standard digital camera on a rover would be the solution to this... But of course, consumer digital cameras are calibrated to lighting conditions faced here on earth. Also they make a picture that is not true color at all, though it is within the brains tolerance, and it seems easy to calibrate the images further. But for images of an alien environment, it is not that easy, you don't have personal experience(or the camera developer teams experience rather) to lean on. If someone shows you a picture of an environment you are familiar with, you may get a feeling of how close it is to reality in color. But if you are not familiar with it, you couldnt do this, you might even feel that the colors in the image must be wrong, even when they aren't...

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Game over, you lose, we hope you enjoyed playing the exciting game of Thermodynamics...