Thanks Jacob, and anyone else who contributed to this thread.

After trying dozens of Vim color schemes, both popular and obscure, I
eventually picked zeburn[1], with oceandeep[2] a close second.

These two color schemes had the highest level of syntactical
differentiation out of the box (there are several other schemes on
that level, but I couldn't find any higher level). Still some place
for Ruby-specific improvements by customization, e.g. define a
different color for instance vs. class variables, which Vim actually
recognizes as two different syntactical elements: rubyInstanceVariable
vs rubyClassVarible. Vanilla zenburn and oceandeep link both highlight
groups to rubyIdentifier, thus failing to visually differentiate them.

I've spent quite a few hours coding in zenburn in the last few days,
and it is indeed easy on the eyes for long coding sessions. I've yet
to test oceandeep extensively.

-Alder

[1] http://www.vim.org/scripts/script.php?script_id=415
[2] http://www.vim.org/scripts/script.php?script_id=368