Updated docstring for DataFrame.plot.bar graph clearify the use of color list
- [X] closes #31691 
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@MarcoGorelli Some of the tests are timing out for some reason. I am not sure why this is the case.
. CI failure is unrelated

I'll leave this open for a bit in case others have comments Thanks @ankushduacodes 