I think a sudden change like you indicate points to a component failure
rather than a weak tube as the tubes tend to lose emmission more slowly
over
time. A green/pink picture might indicate a failed blue video output
device.
Swapping the RGB connectors on the CRT neck might help in diagnosis.
You don't say which model but there are some Sony schematics available
here
http://rv6llh.rsuh.ru/shema2.htm
Other posters may know of others.
Pete

I would agree with Pete's assessment. Sams Fotofacts are usually my first
choice for schematics.
Warning: Sonys can be a pain in the a*s to fix! smile
John