This annoyance has crept into my system some time ago and I can not
figure out how to banish it.

I've looked through all the personal and sysem config files and can not
find a switch to tern off text colourisation.

All I want or need vi for is a simple black text on white(grey
actually) editor. I have no problem configuring that for xterms.

I do not need or want different coloured text, which always gets in the
road on simple editing tasks.

TIA.

FWIW I use *edit when I can use colours for bracket matching, level,
etc, as in latex.