It should be detecting the size of your monitor by the amount of pixels on the Y plain... So if it detects, for example, 1080 pixels for the height from your video mode then it will show up as yellow, and when you click that button it will set the settings to 1080X1920 and change the full screen option to true (or on as I put it in the settings window). Anything higher than that will be red and will not be select-able. So if you don't have your monitor settings to display at 1080X1920, then that will not be available for that monitor. I was trying to get some Multi-Monitor support working, but couldn't not just due to time, but the limitation of the libraries I'm currently using. So my advice is check your display settings to see what your system is putting up on your monitor. If you can't get it above a resolution like 900X1600 then you shouldn't be trying to run the game at 1080p.