*sh: switch to more readable colors for ag

Regrettably ITERM_PROFILE won't make it through to my dev server, which
is why I'm putting the default colors in a loose `else` branch (which
will give me the right colors most of the time).
Vim: tweak search highlighting

I find the garish yellow to be very hard to look at; it gives me an
almost uncontrollable urge to hit `:noh`, even if I am in the middle of
a search and know I'll have to hit `n` again within milliseconds.

Hopefully this blue will be easier to stomach. Seems to look good in
both light and dark Solarized variants.
Vim: simplify dynamically updated regions in UltiSnips snippets

I was doing this the hard way for no good reason.