I tried a safe start and restarting, I tried removing all start up items, none of these worked but every time I restarted a little picture of the monitor flashed up just long enough for me to read that it said contrast increase on. However when I checked under accessibility this was not checked. Tried checking and unchecking and restarting with different preferences selected and each time it didn't fix the issue and the same little screen kept flashing up on start up. So I reset the NVRAM, then I rechecked and unticked the check mark again. Then I restarted again and it went back to normal. So I'm thinking something glitched when I updated to the latest version. Seems to be ok now, just in time too after working a day with the contrast turned up to 100 my eyes are hanging out of their sockets.