I could find no picture of Ben Mayer's projector, but the end effect could probably be accomplished with two projectors of the same model: one projecting the color standard, the other a live image of the paint. The image used as the color standard should be a photo taken of "good" paint at the same location on the factory floor so that the image had the same lighting, camera angle, texture, etc. It seems to me an overlap of the two images might serve as an indicator of the two colors matching: If no discernible color change in the middle, the paint would match the standard.
If you are interested, images of the pre-Ben Mayer blink comparator can be found by searching for images using the phrase "Blink Comparator Used to Discover Pluto."
I hope this helps.