If you are working on a wiring system that has (or soon will have!)
mixed old and new wiring colours, what should you do about colours of
sleeving to indicate switched lives in junction boxes/switches? Are
there rules about this?

My inclination is to fit brown sleeving where there are new cables, and
red where there are old, which seems the best way of avoiding confusion
to anybody looking at the wiring in the future. Or should it be brown
sleeving throughout? (I'm not suggesting systematically changing red
sleeving to brown all through the house, just for example when a new
accessory is being wired in).

Thanks
David