I have used this same setup and cable with my other Scart TV with no problems at all (i even tested it with the other TV directly after getting this issue), thats what made me think this problem could be from the TV itself.
I am using a simple pattern with 100 Ohms resistor to bring down the voltage from 5V to about 2V on Pin 16(Blanking).
rjpe what do u use the other resistors for ? could u explain your pinout and how the resistors changed the colors exactly.