The main page of the site now appears to me as depicted below:
The first and third question there have a blue/cyan title: I supposed that it denotes that a question has been recently modified, but that's not the case, indeed the second question in the list as been modified too but it has the classical color (darker than the normal one since I visualized it).
What does this coloring mean?
This was indeed a bug, and theme colors have been restored. Staff Dan Cormier reports:
This issue was caused by a non-theme color being set on watched post summary titles in a recent design system change. We've reverted that change and shipped the reversion. Thanks for the report!
The blue title indicates a question has a tag that you are watching. The reason for the change, along with the darkening of the "answer" green, is for increased visual accessibility.
