grub highlighting in vi(m)

[Robert G. (Doc) Savage]

When I was editing my /etc/fstab this morning, I noticed there are at
least two defined fs_mntops values which vim displays differently than
others. Most defined values in the fs_type and fs_mntops fields are
green, but 'loop' and 'users' are either white on a red background (if
the first option) or white on the default background (if not the first
option).
 
What file controls the color displays of these reserved words?
 
--Doc Savage
  Fairview Heights, IL