It needs the CRT Degaussed.
It's supposed to do it automatically every time it's turned on cold, but their could be something wrong with the Degauss circuit, or the tube could be magnetized to an extent that the internal degauss coil can't fix it, if that's the case you will need to use an external degaussing coil like this one:
http://www.ebay.com/itm/GSG-Televisi...item5b0ff860df
Another possibility is the Shadow Mask inside the CRT is damaged, this can happen if the set was dropped or knocked over at some point, there's no fix for that except a new tube.