Since upgrading to 2.9.0.beta4, one member of our forum has reported that they are experiencing a similar issue with emails sent from the forum. Their PC is set to Dark mode, they are using Microsoft Outlook on Windows 10.
They forwarded one of the emails to their IT manager and the light grey text was black on the IT manager’s device.
The setting ‘default dark mode color scheme id’ in the forum is set to None. There is only one active theme: Default, the color palette is Light (default), no Custom CSS/HTML.