Using different programs for diagrams within one single document can be a never ending story of unmatching graphics. For example, matplotlib used a different interpolation method for colormaps than pgfplots. Disregarding alpha components, the following script produces a matching colormap. Just specify the matplotlib colormap name as command line argument and you will get a lengthy output that can be pasted to your LaTeX document. The resulting colorbars will at least look very similar:
#!/usr/bin/env python # system modules import sys # third-party modules import matplotlib.cm as cm if len(sys.argv) != 2: print 'Usage: %s colormap' % sys.argv[0] exit(1) try: c = cm.get_cmap(sys.argv[1]) except: print 'Colormap not found' exit(2) print '\pgfplotsset{colormap={%s}{[1pt]' % sys.argv[1] for i in range(101): print 'rgb(%spt)=%s;' % (i, c(i/100.0)[0:3]) print '}}'