Plot uses incorrect colors when columns have the same name

[stevenmanton]

It seems like the plot function jumbles up the colors when columns in a DataFrame have the same name:

pd.concat([pd.DataFrame({'b': [0, 1, 0], 'a': [1, 2, 3]}), pd.DataFrame({'a': [2, 4, 6]})], axis=1).plot();

[jorisvandenbossche]

This seems to work correctly on current master. But we could add a test to make sure it keeps working.

[gabrielvf1]

I have checked and the code at the master really works fine, check the printscreen i tooked:

Now Im going to make a test to check if everything is correct at the graphic before it plots.