200.9 Means of Identification of Terminals.
In devices or utilization equipment with polarized connections, identification of terminals to which a grounded conductor is to be connected shall be substantially white or silver in color. The identification of other terminals shall be of a readily distinguishable different color.
215.12 (C)(1) Feeders Supplied from More Than One Nominal Voltage System.
Where the premises wiring system has feeders supplied from more than one nominal voltage system, each ungrounded conductor of a feeder shall be identified by phase or line and system at all termination, connection, and splice points in compliance with
215.12(C)(1)(a) and (b).
(a)
Means of Identification. The means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means.
(b)
Posting of Identification Means. The method utilized for conductors originating within each feeder panelboard or similar feeder distribution equipment shall be documented in a manner that is readily available or shall be permanently posted at each feeder panelboard or similar feeder distribution equipment.
I don't see anything about needing to keep the blue conductor as A phase everywhere in the system. Only that if there are more than one voltage system (120/208 and 277/480) than they need to retain their color coding through out. In that case, blue would have to be used on only one of the two types and the other type couldn't use blue.