Here's an example of what I'm looking for:

http://www.users.on.net/~markwoodward/vim/linVim/ftplugin/ruby_cols.vim

I can't use this particular one as it is aimed at people who use black
text over white bg, whereas I use white on black.

But I'm sure there are several people here who use Vim in
light-on-dark mode to edit Ruby files, and have defined an apropriate
color set for that purpose.

-Alder