Update $blue variables to match gitlab ui

What does this MR do?

Update $blue- hex values to match what’s in GitLab UI.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

N/A

Security

N/A

/cc @tauriedavis @psimyn