When I used to connect my laptop (running Xubuntu 17.04) to a projector, the color would always be slightly yellow and dim. This did not happen with regular external monitors.
My solution was to use
xcalib. To install:
apt install xcalib
Then, while connnected to the projector, run:
While it's just a hypothesis, I believe what happened was that I was running some program to eliminate blue colors at night, and I still had that running when I first connected to a projector. Then my computer may have permanently associated that color scheme with all external projectors.