If the NEC does not give you colors to use where are you getting that Black, Red, Blue is for 208/120 and Brown, Orange, Yellow is for 277/480. You should always check the wires. If you just went on the colors in a Junction box you could hook your load up to the wrong system voltage voltage.
I am getting that from every EC I ever worked for, since 1976. General procedure was always BRB for 120/208 and BOY for 277/480. 240 Delta was orange high leg & black, red or blue for the other 2. White for LV neutral & grey for HV neutral.
Yes, I am fully aware that circuits should be verified. But if I see wiring done in a consistent, logical manner, I may not have to sniff under quite as many rocks. You have obviously never done service work. If you had, you would appreciate consistency.
Speaking of purples, etc., I would think travellers with any odd colors but I would check them out if not sure.