Most cable I purchase is black-grey-green which I use as hot-neutral-ground. I have a NYY cable that is red-black-grey that I need to use in circuits with the other colors. Is there a preferred way to arrange these colors into the current installation?

See if you can find some green sleeving (or tape) and over-sleeve the ends of the red so you can use that as ground and use black=L and grey=N thus keeping the hot conductors to the local 'standard'.

At least that's how I would do it

Whatever you do leave a note somewhere (in the lid of your distribution board) to remind yourself or inform others.

　

Black is line conductor (L) White or Grey is the Neutral. Green or green/yellow is reserved for earthing conductors only and must NEVER be used for a L or N conductor.

Red is a colour for a phase or line conductor with many standards.

Making allowances for Thailand you could sleeve the ends of the red core with green sleeving at ALL terminations,ie, junction boxes, equipment and socket outlets and the earth bar of the switchboard to identify that it is use as an earthing conductor.

It is preferable to use the correct colour code for earthing conductors if possible.

Thanks. Haven't found green shrink tubing of proper size so I'll wrap all ends of the red wire with green electrical tape.

My view qith thai wiring is now that you should treat it as surgeons in Australia must consider everyone to have HIV as they are not allowed to test anyone. In other wwords whatever the colour you should consider it live. Maybe by trying to apply colour codes you are giving false confidence.

With regard to electrical installations it is normal practice to regard ALL conductors as live until proved otherwise.

Yep -power off - and then use a test screw-driver on every terminal / wire in sight and still proceed with caution.