Please, check this question in Stackoverflow:
http://stackoverflow.com/q/17250392/832621
which motivated this bug report.

The OP identified that when trying to plot using plot_date() the colors are not changed accordingly to the color_cycle specified. Actually they are not changing at all.
With plot() it works perfectly.
I tried to change the colors from plot_date() using:
plt.rc('axes', **{'color_cycle':['r', 'g']})
plt.rcParams['axes.color_cycle']=['r','g']
and
setting the matplotlibrc file to the local folder with axes.color_cycle : r, g.

they all did not work.

thank you very much and congratulations for the great package which Matploblib already is!
Saullo Castro