enhancement: update legend for visualizer

[panteleymonchuk]

Description of change

Change colors and shape for legend.
Closes #1048

Type of change

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• Enhancement (a non-breaking change which adds functionality)

How the change has been tested

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Make sure to provide instructions for the maintainer as well as any relevant configurations.

Change checklist

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• [] 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