The picture on my Sony

Good Day;
A blue picture after it's been on for a bit is normally one of several things. The most common for your Sony is the CRT, tube, the second most common problem is the blue CRT 'IC'(chip). The IC is located is on the blue crt board.
The best way to determine this is to remove the speaker grill(on front of TV), then inner panel, the blue tube will be on your right hand side. Remove that little board at the end of the tube.THIS AFTER YOU HAVE UNPLUGGED THE POWER FROM THE WALL. Plug TV back in turn TV on. If TV comes on with picture and there is no blue in the picture, The tube is bad, if TV turns off it's the IC.
Good Luck, BI.