Patch from ticket #54. This is available in subversion from revision 1047 is in 1.2.5 and 1.3.3.
It simply adds a new config option ".colour" to fields. Use as follows:
foo.label total foo.draw LINE2 foo.colour 000000
NOTE: The use of "rrggbb" instead of "#rrggbb" in the colour field!
You can pick a color either by its HTML code (i.e. six hex digits), or by an index into the palette used. Somehow map the entry to a number, then use "<field>.colour COLOUR<n>" where "<n>" is that number. (requires munin 2.0)