First, carefully read NEC 90.1(A) and (B). "This Code is not intended as an instruction manual for untrained persons". One should not read NEC as a novice and pop up with "What's this? What's this?" questions. It's also off-topic here; questions here must have a basis in a real world problem related to residential.
One should obtain proper training materials. For starters, DIY how-to books found at your local library. Once you have exracted everything from them, perhaps Mike Holt (the paid-for materials, not the forum) - but for 99% of DIYers there's no reason to go beyond the DIY books + forums like this one for what they don't cover.
90.B also says "Compliance results in an installation that is not necessarily efficient, convenient or adequate for good service". In other words, NEC is slumlord bare minimum for safety, it is NOT a design guide or best practice. Creating real usability is up to you.
Conductors must be marked
ALL conductors most be natively colored, or marked, to distinguish 3 classes of wire from one another:
- Grounds: Green, yellow/green, or bare.
- Neutral: White or gray
- Hot: all other colors
Really? There are no other color requirements???
Really. You are set to establish your own color standards. In household/residential, there is almost never a need to distinguish the 2 hot wires from each other, so black-black is fine. In fact it is helpful if you have 3-4 circuits in a conduit, then the other 3 circuits can be red-red, blue-blue and orange-orange, or what have you on the truck.
Wiring Prince's house with 120/208V? Purple, pink, black, white. The only requirement is that colors be consistent within your installation.
Likewise in 3-phase it is often not important to distinguish one phase from another. So again black-black-black is fine. Your second circuit could be orange-orange-orange or even orange-red-brown if you're feeling autumnal. After all, they're all the same voltage just differently phased.
However, if you are trying to synchronize 3-phase motors to all run in the same direction (or the correct direction), you may regret a choice like black-black-black LOL. Like I said up top, NEC doesn't cover usability.
Popular color schemes are black-blue-red and orange-yellow-brown. But these are "conventions" not requirements. Note orange mentioned several times here.
... Except for "wild-leg delta"
However, there is one special type of 3-phase. It contains standard split-phase 120/240V with neutral in the middle, and adds a 3rd phase in a "delta" arrangement positioned 240V from the existing two "phases". Thus, it is 208V from neutral - higher voltage than the other two phases. Suddenly we care.
So NEC has a rule that in wild-leg delta installations, the wild-leg must be orange. (implying the other 2 phases cannot be orange).
That rounds out our coverage of NEC color codes. Really. That's it.
NEC is silent on the use of orange in other installations. So it's absolutely legit to have a 3-phase that is orange-orange-orange, so long as it's not a wild-leg. Or orange-yellow-brown is actually a popular color coding for equal-leg-voltage 3-phase installations. And of course a split-phase circuit can be orange-black-white if you prefer.
However again, due to the "consistent within your installation" rule, an installation that does have wild-leg 3-phase and other equal-leg services too should abstain from using orange anywhere but the wild-leg. Thus their 277/480V should be something like yellow-brown-not orange.