[CONFIG] Implements entries_color validation

[HorlogeSkynet]

Closes #160.

How has this been tested ?

Unit tests + locally.

Types of changes :

• Bug fix (non-breaking change which fixes an issue)
• Typo / style fix (non-breaking change which improves readability)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist :

• [IF NEEDED] I have updated the README.md file accordingly ;
• [IF NEEDED] I have updated the test cases (which pass) accordingly ;
• [IF BREAKING] This pull request targets next Archey version branch ;
• My changes looks good ;
• I agree that my code may be modified in the future ;
• My code follows the code style of this project (PEP8).

[HorlogeSkynet]

Up @ingrinder please ! Does entries_color validation correspond to your expectations ?
Thanks, bye 🙇