If I have the Custom Color setting disabled Globally.
Then I set the Custom Color setting enabled to a specific game, that IS registered and showing up as playing.
The setting will overwrite the Global setting.
So for instance, if I set the Contrast higher in a certain game and then I alt+tab out to the desktop. I can literally see the Global Setting changed to my game setting.
If I reset the Global back to default and the go back into my game, my game settings will have reset as well.
It seems though when I exit the game, the global settings will go back to what I set them. So it just seems that Alt+tabbing doesn't switching the display settings