Gitlab Email Diffs not formatted

I am running two instances of gitlab.

People who are using them are reporting that one instance sends out ‘git diff emails’ with formatted text e.g. green for new content and red for removed content etc.

The other instance seems to send only plain-text or unformatted content.

Is there an option where to configure this? Thanks in advance!

It seems it was caused by Enable multipart emails which was disabled in one of the instances.