feat: improve block colors in visualizer nova

[VmMad]

Description of change

Fixes #1414

Type of change

• Enhancement

How the change has been tested

Describe the tests that you ran to verify your changes.

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Change checklist

Add an x to the boxes that are relevant to your changes, and delete any items that are not.

• My code follows the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• 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