Hi Pengrus, I now understand why you had the add-on problem. Thing is, the add-on uses two files that reside in the templates/darkmatter directory. If it doesn't find those files it cannot do it's job. I will make some changes to it that display an error message explaining what's going on to the user to make this more obvious.
As for the about page: The CSS rule is:
You could change it to #ccc for example to make it lighter.
Hope this helps!