I see a focus here on the use of cable. I didn't mean to limit the discussion to cable. Here are some thoughts I have heard expressed for when pipe is used:
"I use red for the switch leg, even for 277v systems, because most switch wiring diagrams use red for the load side."
"You go 'one color up' for the switch leg. For example, if your phase color is red, then blue is your switch leg."
"You MUST use the same color as for the line side, as the code requires all conductors on that phase to be the same color."
"I try to use a 'weak' color .... that is, pink for the switched leg if the phase color is red, violet if it is blue, so the color is different, yet clearly associated with the phase color."
"I use the phase color, but tape the ends to match the switch diagram / pigtails." (This might be THE way to do it with the newer electronic switches, which require an entirely different approach to wiring a switch).
Please note that last comment; especially with 3- and 4-way switching, what you learned in the past is often incorrect, and will blow up a $130+ switch. You no longer have 'travelers' as you know them.
(BTW ... has anyone else been getting wire where the 'black' looks like a dark gray ... and the gray looks really dark? This can be confusing!)
