When you turn on Your Computer, if you observe color patches on the screen that is due to magnetic fields around the monitor like Speakers, Surge protectors developed the color distortion on the monitor display.
Why Color Patches are appearing on the Screen ?
You have to know that Earth is it self a natural magnetic field and magnetic objects around monitor can build magnetization in your monitor which causes the color distortion.
What type of Monitors affect due to Magnetic Fields?
Only CRT monitors get magnetized, latest LCD, Plasma monitors doesn’t get magnetized, because they don’t have a CRT in them.
What’s the Fix?
There is a degauss button available on the main screen which looks like the Horseshoe, selecting it once will clear the color patches on the Screen. The latest CRT monitors have inbuilt Degauss, whenever you power on your Monitor, it will automatically degausses. Make sure speakers, magnetic objects are away from your Monitor.