A simple question but I am afraid that nothing in heraldry or the study of the symbolism of flags is ever black and white.

or sable and silver.

Grumpy I wouldn't argue with the OC of 41 Sig Sqdn, if grey is what the Kensingtons wanted it was what the Kensingtons had/got !

Not arguing: it is clearly grey, and is clearly what they want.

My understanding is that there are / used to be rules about these things [like never putting a colour next to a colour] so are the rules being obeyed or ignored in this case?

The Union flag is a good example of the colour/colour rule ..... white is not a "colour"

Just asking for an expert to contribute.

Mjr Whittle took my attestation.
I wonder if the colours are non heraldic and that they grew from the rifle regiments and volunteers. The badge was a coat of arms of the borough...

The colours were those of the pre 1908 RVC uniforms which the 13th Londons retained. Nothing heraldic about them.

That is not my point, which was that there are or were rules for heraldry and rules for flags, usually followed in Great Britain by the military. Is grey an officially permitted colour?

That seems a valid question, albeit asked out of curiosity.