to make things more confusing, i would never use the term vermilion for red ink!
the ink might be vermilion (red), but generally in US, one speaks of red ink -- in accounting red ink is sometimes used to record a loss, so businesses in financial trouble are sometimes said to be "swimming in red ink".
in the context, it was quite clear that vermilion meant red ink, but i would not generally substitute one for the other in commonly spoken english.
Still one of the joys of english is is flexibility. I am sure everyone understood the statement, but i suspect most would agree with me, in saying they have nevered used the word vermilion (by itself!) to mean red ink.
the use of red ink might be implied, ("the vermilion lettering stood out", but if asked about them, most would say the vermilion letters on the page were made with red ink, not that they were made with vermilion.
vermillion is used almost exclusively as a color (a specific shade of dark red).
likewise, it might be "as dark as midnight" (very dark!) but to describe the sky or ceiling, we would say the ceiling was painted midnight blue.--making it very clear that 'midnight' in the second sample is a color.
It was as dark as midnight when we entered and the flashlight did little to break the darkness, though it did help us find a light switch. Even with the lights on, the room remained very somber. There was very little reflected light; the walls were covered with books and the ceiling was painted a midnight blue.
anding to all this confusing, there are exceptions! (but of course, i can't think of any right now...
