Created Border for color examples

[jeetvora331]

PR Summary

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and pydocstyle<4 and run flake8 --docstring-convention=all).
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

[jklymak]

I think we already had a PR that did this? I guess that was #16467 and it didn't actually implement the border color...

[story645]

@jklymak yeah there was debate around borders so we decided was easier to just leave it to another PR.
Thanks @jeetvora331, I think the light gray is neutral enough that it's not messing w/ the color perception too much.

[jklymak]

Thanks @jeetvora331 !