Imac screen problems

So yesterday, my screen started to act crazy and just start changing colors and all on it's own. I unplugged everything and plugged it back up, still did it. So i restarted a few times, and reset the NVRAM just cause. Then it turned on and was just fine. This morning, I turned it on and it's the normal startup screen and then goes purple and completely white. Does anyone know how to fix this problem or what I need to do?