BUG: Extra color introduced with plot.

[wuhaochen]

User reported in StackOverflow: https://stackoverflow.com/questions/49887076/matplotlib-error-while-coloring-barplot-with-list#49887076

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

df = pd.DataFrame(np.abs(np.random.randn(48, 4)), columns=list("ABCD"))

color_list = plt.cm.gnuplot(np.linspace(0,1,16))

df.A.plot.bar( figsize=(16,7), color=color_list)
plt.axvline(15.5, c="black", lw=1)
plt.axvline(31.5, c="black", lw=1)
plt.plot()

Problem description

This bug happens when single color is needed for plotting but an array is provided.
In the end of _get_standard_colors function in plotting/_style.py. An extra first item will be added to the color array which caused the circular misbehaved in such case.

Expected Output

The bar 17 should have the same color as the bar 1.

[wuhaochen]

I can send a PR to fix this.

[anushreejain98]

*error:this line has been written twice,removing may fix it

plt.axvline(15.5, c="black", lw=1)
plt.axvline(31.5, c="black", lw=1)

[wuhaochen]

This is a confirmed bug, the lines you pointed out are used to plot the two separating vertical lines and they are irrelevant to the bug.