Remove explicitly set background on board blocks

Description

This removes the explicitly-set background on the board blocks to use the default background color of the terminal.

Fixes #15

How Has This Been Tested?

See before:

After:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules