4 AWG and bigger

In the past it was much more difficult to get an insulation other than black for conductors 4 and larger.
Still is at many suppliers, especially as you go even larger.

I always thought that it was to avoid burdening contractors and manufacturers with extra cost once it was easier to distinguish the circuit and more likely that a qualified person would be working on it.
 
What I mean is you can’t re-identify a conductor smaller than a 6 AWG per 200.6, but you can do the reverse for ungrounded conductors per 210.5.
So if the identification would come off the re-identified ungrounded conductor, you would still know that it is an ungrounded conductor and there is no real hazard. If the identification would come off a black conductor re-identified as a grounded conductor, you no longer know it is a grounded conductor.
 
Around me, most of the supply houses have colors through 500 kcmil
My larger supplier that delivers from 20 miles awag would have all that, but my local smaller go-to-in-a-hurry store would not. The orange store apparently does not sell red larger than #2, although they go up to 3/0 Cu and 4/0 Al in black. So yeah YMMV but black is still going to be more readily available once you get to 4awg and above.
 
Around me, most of the supply houses have colors through 500 kcmil
I have a supplier that has colors in larger sizes, but they often need to bring them in from a more centralized warehouse and takes a day or two. They may have white and green up to maybe 2 AWG in local warehouse but mostly just black otherwise
 
Adding to the confusion is that a lot of tray cable isn't made in colors you would expect. Some 12/3 is black, red, blue. No additional ground either bare or green. No white or grey for neutral, so at lease 2 wires have to be color marked, sometimes all 3 if trying to stay totally correct in panel. Various other colors too in 4 and 5 wire cables. IMHO, 12/3 should be black, white and green, suitable for 120 volt as is. Some coloring for 208 or 277.
 
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