My current job has all manner of $100+ "light switches" and other fancy stuff. Not all of these use "traditional" wire arrangements; the 3-way arrangements are not wired at all as a traditional 3-way would be wired.
This has brought some interesting practices to light, as everyone seems to swear by a different 'trade practice' when it comes to identifying those wires that are neither "always hot" nor neutrals.
What means do you use to identify these "other" wires, if any?
Assuming cable, three wires in a box the black is common. Five wires in the box, the black from the two wire cable is common and the white is neutral. Where the travellers are connected in a box, they are connected red to white.
If it's someone else's work, it could be anything.
In Austria the situation is AFAIK slightly different because blue is no longer acceptable for anything but neutrals (except in systems without a neutral, e.g. 133/230 V 3-phase) but generally conductors such as travellers or switch legs are considered phase conductors and colour-coded accordingly. In conduit jobs, colours such as orange, purple, white or red are commonly used to identify such conductors. Cable is always brown, black and grey for phases and re-identification is usually not required, it's up to anyone working on the installation to understand the purpose of those wires.
In the US, if you are identifying the white wire on a switch leg, it should be the hot going down to the switch. Now that it is required to have a neutral in the switch box, I am not sure how you wire a 3/4 way dead end switch leg unless you have 4 wires plus ground going down there. I think they are pretty much mandating in line switch wiring where the hot comes in one end of the series and the light connection goes out the other end. I suppose you could use 3p "full boat" cable or 2+2 Romex.
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!)
As I said, with pipe I use anything that isn't already used and that's acceptable as a phase. The full list of (easily available) phase colours in Austria is: - black - brown - grey - white - orange - purple
The first three are the official recommendation for phases (L1 brown, L2 black, L3 grey) but can be used differently. In domestic conduit jobs I frequently see 3 black phases. Red is in theory an acceptable phase colour too but frowned upon because it used to be earth (ground) until 1965. Many electricians will even tell you that red may not be used for mains wiring at all and red earths have to be replaced as soon as you touch the wiring. Of course that's not correct but many strongly believe in that theory. Yellow and green are available but explicitly not to be used outside factory-wired equipment because either could be confused with yellow/green.
Probably the most common colours for switch legs, travellers and other non-standard stuff (e.g. control wiring from push-buttons to 230 V operated latching relays, which are highly popular whenever a light is to be switched from more than two points, most sparks won't do 4-ways unless specifically told to) are orange and purple. Most contractors I've experienced will only have black, blue, yellow/green, orange and purple 1.5 mm2 in their vans, larger sizes only as required and usually only the first three plus brown 6 and 10 mm2 (required for load side meter tails).