First check that the TV has no external loudspeakers near it, as they contain strong magnets which can affect the colour.
However, more likely is that a part named a 'positor' has failed, allowing the shadowmask to remain affected by residual magnetic field. This is not a diy job. It requires this specific part, which is usually safety specified.
The good news is it's a five minute job and should be about as inexpensive a tv repair as you can get.
Cobweb, November 2007
