Switch to a11y Colors

[zackkrida]

Fixes

Fixes #455 by @ayanchoudhary
Fixes #454 by @ayanchoudhary
Fixes #476 by @ayanchoudhary
Fixes #519 by @zackkrida

Description

Switches our colors over to their accessible replacements, and updates vocabulary stories to match. Adds a new color brighter-dark-slate-blue, all other colors are replacements of existing colors.

Technical details

Tests

Screenshots

before

after

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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