Add new flymake color

[yuezhu]

This PR adds new flymake colors based on the existing legacy flymake color schema:

Before

After

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• [x] The commits are consistent with our contribution guidelines
• [x] You've added a before/after screenshot illustrating visually your changes.
• [ ] You've updated the changelog (if adding/changing user-visible functionality - e.g. theme new faces/packages, changing existing faces, etc)
• [ ] You've updated the readme (if adding/changing configuration options)

Thanks!

[bbatsov]

Thanks!