draft: coloring using matplotlib normalizations

[ChristopherRussell]

Summary

Thank you for contributing to great_tables... this is great! To make this process easier for everyone, please explain the context and purpose of your contribution. Also, list the changes made to the existing code or documentation.

Related GitHub Issues and PRs

• Ref: #

Checklist

• [x] I understand and agree to the Code of Conduct.
• [x] I have followed the Style Guide for Python Code as best as possible for the submitted code.
• [ ] I have added pytest unit tests for any new functionality.

[ChristopherRussell]

This is a draft / to share ideas referenced in #192