Picture background is Red Sony KP-57wv700
Is it a reddish tint or the picture is just red? Did it just happened, or you are just noticing a gradual change?
Reddish tint: Blue and/or green CRTs are getting weaker. More likely the green CRT. Unplug the unit and somehow remove the back cover, etc. to get a direct view of the CRTs. Use a flashlight to inspect each CRT through its lens. CRTs with excessive wear will show a definite "burn" mark where the picture forms. Compare the center CRT (green) with the other ones. Normal wear in all three tubes is expected. What is important is to notice the difference. A significant wear in one means it has to be replaced, but usually all three have to be replaced in order to get the right purity. This is a major overhaul, and unless the TV has a sentimental value, it's not worth it.
Picture just red: Green and blue CRTs not firing. This is easily observed by running the TV with the back cover removed. Probably a loose connection, but you will need the manual to trace it. You could gently tap the chassis while the TV is running and see if this restores the blue and green CRTs.