On #1 - I know it sounds a little odd, but it makes sense after thinking about it for awhile. Using the White conductor for the "Line" to the switch would fall in the lines of the "Common" part of the loop. Also, if the loop is for a simple 1 pole switch and the branch circuit is feeding into the light outlet, the spliced wires in the light outlet box will automatically have only one Black wire for the switch leg, and hopefully all the branch circuit "Neutrals" get spliced with a pigtail for the luminare [light fixture].
Heard mention that at some time, the NEC requested the OPPOSITE connection scheme - but still re-identified the White wire [any color except White, Gray, or Green tape/paint/etc.]. Not sure when this took place, or if it's true! Maybe someone can chime in with an answer.
For #2, the color code being mentioned is simply one that is preferred in the field.
The colors used for 277 VAC Multiwire circuits [4 wire] would be:
A: Brown, B: Orange [or Purple], C: Yellow, "N": Gray.
For simple 277 VAC 1 phase 2 wire circuits, this equals out to be:
A: Brown / Gray,
B: Orange [or Purple] / Gray,
C: Yellow / Gray.
On the same system [480Y/277 3ph 4wire], L-L colors could be:
480 VAC 1ph 2 wire:
Brown / Orange [or Purple], Orange [or Purple] / Yellow, Brown / Yellow.
480 VAC 3ph 3 wire:
Brown / Orange [or Purple] / Yellow.
However, it has been common [for me at least], to just follow the "Black / Red / Blue" color scheme for L-L or 3ph 3 wire circuits regardless of system type [unless situations require different].
These color codes are something that needs to be "agreed upon" by everyone involved on that particular installation, in order to keep things uniform.
I am sure you know of this, plus it's been mentioned here, but the color codes we use in the field are mostly just trade preferred schemes.
The NEC only limits colors to use of White, Gray, Green, Green w/"tracer", Bare [uninsulated] and "sometimes" Orange [4 wire Delta], on general low voltage power systems of 120 VAC upto 600 VAC. I wanted to be sure and include this redundant statement just for clarity regarding color codes.
Although you could install all Black ungrounded conductors on any of these systems - such as a job with 480Y/277 3ph 4 wire and 208Y/120 3ph 4 wire - and still be in compliance with the NEC, you would get a lot of flack and strange looks from others in the trade.
Hopefully this message and others will answer your original questions with minimal corn-fusion [confusion]