We’ve found many posts about similar issues (such as: CF7 Response is Always Warning Colour in 5.2+).
We use Pro 7.3.9 and didn’t see anything in the changelogs fixing it, so either the theme overrides the proper CSS somehow or we did some accidental global CSS on our 100+ sites.
To reproduce the issue, you can fill out this form (I’ll be the only one receiving the resulting emails): https://www.magikweb.ca/contactez-nous
Thank you for any lead!