Clean up colors documentation to be more clear about MD2/MD3

[manojleaton]

Fixes #BLUI-5762 .

Changes proposed in this Pull Request:

• Updated colors palette documentaion.

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[github-actions[bot]]

Visit the preview URL for this PR (updated for commit d963b0b):

https://blui-doc-it--pr744-feature-5762-clean-u-zmd4mz8g.web.app

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