Notifications mails background color is missing on Microsoft Outlook 2016

STEPS TO REPRODUCE

Preconditions: The XWiki instance has the Mail Sending configured. An user (e.g. U1) is created and has a valid e-mail address set on its profile (e.g. a Gmail one).

1. Configure Microsoft Outlook 2016 with the (valid) email account used by user U1
2. Login as user (U1)
3. Go to Notifications > Settings and set all Pages Notifications to ON (both menu and email)
4. Watch the wiki
5. Login as Admin
6. Create/update/comment a page
7. Trigger the 'Notifications daily email' job from Scheduler.WebHome
8. Go to Outlook 2016 and observe the mail received on the user's account

EXPECTED RESULTS

The Notifications mail received has a grey background (similar with the one when accessing the email address from the browser - e.g. Chrome or Firefox).

ACTUAL RESULTS

The Notifications mail has a white background instead which can prevent the proper display of the logo (if this is white as well or even light colored).