Hi Spectre,
Sorry but I confirm the service engineer's thoughts !!!
Red and blue patches are symptomatic of a mask default (sometimes, patches are clear brown, almost yellow).
The mask is a thin black film with small holes wich is pasted on the internal side of the screen.
If the mask had shifted, some 'chromophores' (red, blue and green), that make the picture, are no more excited by the electron gun (because some holes are no more in front of the 'chromophores').
The only solution is to replace the tube

.
Accessing the service menu will not be efficient because this is not all the picture which is red or blue.
Bye.