This is how notification looked before PR https://github.com/Automattic/wp-calypso/pull/17796 _"Update notice colors to pass WCAG AA guidelines"_:

This is how it looks today:

Seems to boil down to the fact that there's some custom css modifying that sync notice.
See how Notices normally look like (choose "Compact Notices").
Checking out an issue about inline notice styles might be relevant.
/cc @jameskoster
I could send a quick PR to fix this.
Would regular just <p></p> suffice? Notice element doesn't seem to have any ARIA attributes that we'd be missing (tho it might have them in future).
If design change would be okay, a quick fix would be make it look like either one of these:

...or even like <FormSettingExplanation>:

In my opinion, it probably shouldn't be a Notice. I haven't viewed the whole context of the page, but your suggestion to just use gray text seems good to me.
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In my opinion, it probably shouldn't be a Notice. I haven't viewed the whole context of the page, but your suggestion to just use gray text seems good to me.