With a new release there was an option to be able to allow users to change the theme on viewing the forums. You may have noticed this within the preferences panel of your profile here on the forums. I have recently added a few themes to this to allow you to choose from on the site.
Once there you can choose from a few different themes and can set this to default on all devices or just the one you are currently using.
Here are some screens of the other themes I have uploaded.
(This is what the GRG theme is based on)
I will add more when others become available