Improve ping/highlight colour notification

[kittykat]

Your use case

What would you like to do?

Change ping/highlight colour.

Why would you like to do it?

• Red is a jarring colour
• Red is a poor choice for red/* colourblind users

How would you like to achieve it?

• Change default ping colour - Improve default ping colour in timeline (currently red) #441
• Invert colour (from theme?) - Option for highlights to be inverted rather than relying on red-for-danger, as they fail with R/G colorblindness #1655
• Add a user setting to chose ping colour - Ability to change ping color #6520

Pre-development checks

• Tagged as T-Enhancement and with correct A-* label
• Product team confirmed that this feature:
  • …is on the roadmap or
  • …could be added to the roadmap or developed by a community member
• Final design has been approved by the Element design team and attached to this issue:
• Acceptance criteria:
  • Default colour of pings is changed to be not as jarring
  • Default colour can be changed by users

[kittykat]

Major because it could cause missed notifications for people who have colourblindness

[janogarcia]

@rufuskahler Will be addressed by the new color system in the works as for #23302 (comment) 👍

[daniellekirkwood]

We've completed the colour pass and the Red has shifted tone (and will continue to be iterated on with other tracks of work). All the linked issues are closed so I'm going to close this as complete for now.