DataFrame.plot doesn't use kwarg color properly
When we use df.plot(kind='bar), each bar has a different color and it's ok, but not if we use df.plot(kind='bar, color='rgbc') for example, or each custom colormap, because all bars in a particular group have the same color.
A quick workaround, in plotting.py, line 716, replace
if 'color' not in kwds:
    kwds['color'] = colors[i % len(colors)]

by
if 'color' not in kwds:
    kwds['color'] = colors[i % len(colors)]
else:
    kwds['color'] = kwds['color'][i % len(kwds['color'])]
