"Ah, Daniel-san, you too much TV!"

Thanks, Larry. I sorta half remembered that was what happened but didn't want to say it if it wasn't true. It'll be easier to remember now.

This is something that I have had extensive experience with, because of our specialty.

Most televisions have a thermistor in them that allows current to flow to the deguassing coil for only a few seconds before heating up and becomming an almost infinate resistance. As the resistance of the thermistor increases, the strength of the deguassing coil fades out, leaving a neutral magnetic polarity.

The process neutralizes the field only for the position that the television was in while the deguassing process took place. As soon as you move the television, it needs to be degaussed again.

Unfortunately, it is not as easy as just turning the TV off, then back on. The thermistor will have to cool off, which will take a few minutes. After all, the reason they call it a thermistor is because it's resistance depends on it's temperature--more resistance with more temperature. Therefore there is less current and less magnatism from the degausing coil as the set warms up.

If this doesn't correct the problem, there could be a couple of other reasons for the problem. The yoke could be loose, and could move if the set is tipped forward. This problem would be charactorized by the center of the picture being okay, while the colors on the edges, all of the way around, distort in almost a circle. This is not very likely, however.

Another possibility is that there is a loose shadow mask in the tube. This problem is often revealed by other charatoristics-- irratic changes in purity, each time you move it, or changes in the purity as it warms up. I have seen this problem more in Sony tubes than with any other, but it is still unlikely.

Be careful if you manually degause the tube with a degausing coil. The ones that you buy are often powerful, and if you don't know what you're doing, it is possible to damage the shadow mask. Don't hold it directly against the glass.

Frnakly, I don't think you will be able to solve your problem unless you are willing to turn the TV off for a few minutes, then turn it back on, after it is in the desired viewing position.

I suppose you could install a manual degaussing circuit. It seems like it would be pretty easy, as a degaussing circuit is not very complicated.

If none of these ideas work for you and you have to regularly turn the TV while it's on, you may have to go to another technology, like LCD, plasma, or projection. Good luck.

1) Look for and temporarily remove any magnets in proximity of TV. Door catches, for example.
2) Pull all equipment from stand, except TV.
3) If discoloration persists after powering TV back up (degaussing as described above by others) and swiveling, proceed to step 5, otherwise step 4.
4) Replace magnets and/or components one by one with TV on and in position that had been causing greatest discoloration. If reintroduction of given device reults in discoloration, culprit found -- move to location where it causes no harm, or replace. If discoloration does not reappear after putting everything back, congratulate yourself for having resolved problem by no discernable means of your own. Skip next step.
5) Go to sheet metal shop and pick up two or three pieces of steel sheet (perhaps galvanized), about 30"-36" square and maybe around 16-18 gauge. (Look in their scrap bin, and don't cut yourself!) Try placing sheets adjacent to TV: under, over, to either side, rear, or some combination of above. If problem goes away, congratulate yourself on having blocked mysterious source of high ambient magnetic flux. Consider moving. Or at least find way to mount steel sheets and render aesthetically acceptable. If problem persists, give up and get new TV. Maybe not another 27" Sony. Maybe not CRT at all.
End)

As others have commented, there is an external (to the TV) magnetic field.

Is this a metal stand? It is possible that some portion of the stand is magnetized.

As a diagnostic, move things around. You don't have to (re)move anything, just move each item slightly while observing the screen. When you move the trouble maker, the discoloration will change.

Another type of diagnostic could be done with a sheet of iron, an iron skillet, or an iron tool of some sort. (hopefully it will not be magnetized) Steel is not always the best choice for this sort of activity. When the iron is inserted between the external magnetic field and the TV, you'll see some sort of change in the discoloration. (Don't expect this to make the problem go away, it's just a diagnostic tool)

I solved this problem on a couple of Wega 36" sets by running a dedicated circuit to it for power. Our repair tech said if the TV is current-restrained at power up, the gegaussing won't work properly (it draws alot of current at the moment of start up). I first tested this by running a 12 guage extension cord from a known dedicated outlet (usually an outlet above the kitchen counters, washing machine outlet, etc.) before going ahead and wiring for a dedicated, home run 20A circuit.
I'll be curious to know if this works in your case, too.
Hope this helps...