Bug: Label text unreadable in dark theme

[wiggin77]

Steps to reproduce the behavior

When using dark theme for Mattermost server, Boards rightly switches to dark theme as well. Card labels remain the color specified by the user, but the label text is based on the theme and becomes unreadable.

Expected behavior

The label text should remain fixed (black) to be readable with the pre-defined label background colors.

Screenshots (optional)

Edition and Platform

• Edition: Community and Hub
• Version: 9.0
• Browser and OS: All