Best way to avoid any color problems when using a TV at an angle is to start with a brand new TV. Install it at the angle you want it before you ever turn it on.
You shouldn't have a problem then.
I don't really understand why, but TVs (and indeed, even many arcade monitors), have a bit of a problem switching orientation or even angle after long periods of use at a different orientation or angle. Sometimes they will never quite get correctly deguassed.