email highlight color too pale

Not sure about "Recent changes". This has been an ongoing complaint for both Legacy and New Outlook for Mac.

https://learn.microsoft.com/en-us/answers/questions/4646761/highlight-color-of-selected-message-in-outlook-for

https://learn.microsoft.com/en-gb/answers/questions/5515092/is-there-a-way-to-increase-contrast-for-selected-m

https://learn.microsoft.com/en-us/answers/questions/5684390/flagged-emails-are-difficult-to-read-in-outlook-fo

You can vote for an comment on this Feature Request if it matches your complain.

https://feedbackportal.microsoft.com/feedback/idea/8cc4caeb-8e8d-f011-8151-6045bdba91e3

(You must "Sign In" at the top right of the Feedback page before you can vote).