Feature request: Allow to set a custom topbar color

Hey :)

In the case of Trello, the topbar color don't change when we are switching to a different board with a different background.
So I managed to force the default topbar color (grey) to the Webby app.

In the .desktop file I replaced 'WebbyThemeColor=#026aa7"' to WebbyThemeColor=#ffffff"', and set the file owner to Root to prevent Webby to edit the file.
But it didn't works. I don't know why but when I launch again the Webby app, the file ownership changed to User.

The idea will be to add custom argument to Webby to disable topbar color detection.
Like 'Exec=webby --no-chameleon https://trello.com'.