===== Original message from John Hunter | Sat, 02 Jul 2005:
Take a look at the help for the matplotlib.colors module at
data represented by a list of x,y0,y1 mapping correspondences.
The two values of y are to allow for discontinuous mapping
it confused me that there are no x values in the colorbrewer
specification, i guess i have to assume even steps, like
diff(x) = 1./8 for an 8-sequence.