You might look through the TV menu for an entry called "Demagnetize" or "Degauss" . Over a period of time, many CRT screens become magnetized. This causes colors to to be off from just a little to "way out there".
Usually, activating this function once or twice will restore the screen. If no such entry appears in your TV menu, you might want to try manual degaussing instead. These devices can be purchased for $15 - $60 and will perform the degaussing quickly. Here is a list
of the devices and where they can be purchased.
Also, check home stereo speakers that may be placed within 2 - 3 feet of the screen. The large magnets inside them can cause picture problems. Remove them to a distance as far as possible from the CRT screen. Speakers that are labeled as "Magnetically Shielded" should not cause this problem - these type are often parts of a home theater speaker system, but not as part of older stereo systems.
Of course, if the settings on the TV have been adjusted - that could be the source, too. Make sure the TV is tuned properly to the channel needed (if not using audio / video cables from the source DVD, cable box, etc.). Dial down the Color, Hue and Tint settings and slowly work them gradually upwards - or locate a one button color or other "scene" selection (Sports, Vivid, Movie, etc.) to see if that solves the problem.
Based on the information you provided, I expect that one of these solutions will solve your problem. It is also possible that one or more electronic components soldered to the circuit boards inside the TV is failing or has failed. If that is the problem - it will require replacement of defective parts - and degaussing will not fix this issue.
I hope this helps and good luck!