Replaced (most) nonstandard colors with official Solarized color values

A small number of nonstandard colors remain.  These were cases where I wasn’t certain what the color affected, or situations where the color is *supposed* to be slightly off—for example: the gutter, or the caret.

Although I can’t test these with every possible language, I’m pretty sure there shouldn’t be any issues with these changes.  As I was working on this, it seemed to me that most of the nonstandard colors were simply an ad-hoc approximation, rather than a deliberate use of “slightly off” colors for situations like the above.