While doing some testing, I went back to the default white background,
and noticed that some of the font-lock colors have rather poor contrast.
I'm not sure if this is partly due to anti-aliasing, but it sure makes
the text difficult to read.

What do people think about making the following changes for the
light-background settings?

 font-lock-builtin-face:  "LightGray" -> "MediumOrchid4"
 font-lock-constant-face: "CadetBlue" -> "dark cyan"
 font-lock-string-face:   "RosyBrown" -> "VioletRed4"
 font-lock-variable-name-face: "DarkGoldenrod" -> "OrangeRed4"

This does not alter the existing color scheme, except for darkening the
fainter colors.  (The dark-background color scheme seems to be fine.)