[LetThereBeColors] Incorrect message colour in light theme

[MMK21Hub]

When the Light theme is selected in appearance options, the text colour for message content is incorrect. It appears that the colour from Dark theme is being preserved.

Steps to Reproduce

1. Switch the app's theme to "Light" in User Settings > Appearance
2. Go back to a channel with some messages
   --> ❌ The message text is light grey, which is difficult to read against the white background.

Expected behaviour

The text would be blank. (This is the case when the plugin is not installed, and the plugin doesn't adjust the default dark theme font colour in this way.)