My opinion, just from the catalogs and what I have seen over the years:

there were two styles of cal 12 Montreals, one style with raised hour markers and one with just luminous strips for hour markers.

The hard info for me comes from Page 20 in the 1974 catalog (below) shows these two variations, and they seem to both come in blue and black, with the raised marker version coming in white as well. There was also definately a gold raised hour marker version (in fact I bought one on ebay about 2 minutes ago).

So for me there was:
110.503 BC blue dial, blue inner bezel ring, blue subreg, flat markers
110.503 NC black dial, black inner bezel ring, black subreg, flat markers
110.503 B blue dial, blue inner bezel, white subreg and seconds track, raised markers
110.503 N black dial, black inner bezel, white subreg and seconds track, raised markers
110.503 W white dial, white inner bezel, black subreg and seconds track, raised markers
110.503 ? gold dial, gold-ish yellow/beige inner bezel, gold subreg and seconds track, raised markers

then there is the black dialed PVD version like 110.503 NC, and the later 7750 movement (?) versions (different story).

I don't believe there where mixed inner bezel /dial colour combos like blue dial, white inner bezel...but I have no way of proving it, except that it looks "wrong" and is not documented anywhere.