Change comment colour to dark green

The original dark grey was simply too dark on my display
Change current-line color to blue-green

Magit uses the current-line face to show the currently selected hunk,
making the near-black default color useless.
Display window borders

It is useful to be able to see the extent of a window, so paint them the
same color as the mode-line.
Define parenthesis highlight colors

It is useful to be able to control the colors of parenthesis
highlighting independently of the rest of the theme.