plt.plot(dates, jec, 'k.', markersize=20)
new_t = np.linspace(min(t), max(t), 80)
new_dates = map(mdates.num2date, new_t)
kinds = 'cubic', 'quadratic', 'slinear', 'nearest', 'linear', 'zero', 4, 5
cmap = plt.get_cmap('jet')
colors = cmap(np.linspace(0, 1.0, len(kinds)))
for kind, color in zip(kinds, colors):
    new_jec = interpolate.interp1d(t, jec, kind=kind)(new_t)
plt.plot(new_t, new_jec, '-', label=str(kind), color=color)
plt.legend(loc='best')
plt.show()
matplotlib большой набор цветов для графиков