This is a common complaint with the colour crt TV's. I had a similercomplaint
with my SONY TV, and I used to regularly complain to my dealer. Later I learnt
that it is caused by the accumulated static current on the CRT or by some
magnetic field close by.
Please remove any speakers or other high current sources near by the TV,
Another thing please put off the Power supply of the TV totally at night or when
you are not going to use it for longer durationd. Even pull out the chord.
The coulor TV's have a cirguitry to deal with this problem, known as degausing.
The degausing circuit gets activated when you put on the power supply of the TV.
or this left over charge gets neuteralised if you keep the supply off for some
time say about half an hour.
Hope this will help you. It did help me.