Color schemes for graphs out of excel can be pretty bland, and there are ways to get aesthetically pleasing color sets with predefined palettes like Tango or COLOURlovers which is a huge repository of color schemes.
However these, or just using linear interpolation between two colors or a color and white don’t do your data justice.
The gist is, colorspace doesn’t match your eyeballs, and equidistance colors in HSL don’t have the same lightness intensity. As best explained in this post over at vis4.
You can jump right in to some color palettes (which are also GIS friendly) at Color Brewer
Here are some more graph libraries worth investigating:
And a bunch of random tools here
And this guy does beautiful things in flash
Also. What you really came looking for: