TST/VIZ: add test for legend colors for DataFrame with duplicate column labels #11136
- [X] closes #11136
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I have just made the changes. Can you check if is everything right now? Really thanks! Fix were made, the for syntax is better now and now im using methods from matplotlib like get_color() and get_legend(). Great thanks @gabrielvf1 