Wiring colors for 'intermediate' connections
Over my many years of engineering, I developed a colour scheme for myself that I thought was obvious. However, arguments with other engineers over 'correct' colours have disabused me of the notion that anything is obvious (witness the international mess over mains wiring colours).

FWIW, I use red as +ve, and usually +5v. Black is usually 0v. If I'm running a +3v as well, that tends to get orange (for 3!) or yellow (a sort of unusual red!)

When I need a -5v, it's blue.

When I need +/- higher voltages, like 10, 12 or 15v for opamp rails, then it's orange and purple. I shouldn't have to spell out which of those is +ve and -ve, it should be 'obvious' (is it?). The 0v wire to weave with those from the PSU is green.

'Unusual' supply voltages, and signal voltages get white or yellow, grey or pink.

That's all if I have the colours to hand. If not, I use whatever.

Mains wiring

Here in europe, we have brown as hot, blue as neutral, green/yellow stripes as earth. In the US, they use white, black and green. Other continents use other colours. A report a decade or two ago came up with 'the one true colour scheme' which had to be (a) obvious (b) colour-blind friendly (c) low-light friendly (d) different to all the other existing colour schemes, which is white for hot, grey for neutral and black for ground. I think it's obvious and a great idea, but it's not going to catch on, not least because it would electrocute 90% of americans.