Whenever I load a forum that has a bright or light color theme, it instantly makes me feel good and I spend more time on the site. Though many sites that have darker themes are attractive, I don't spend much time on them. I don't mind a dark header or background but prefer main content to be light color or white as it helps for reading. What is your preference for forum theme color for your own forum or forums you visit?
I think it's good to have both. A light theme is essential when you're viewing the forum on a mobile device, but a dark theme is softer on the eye in low light.
There are many individuals that prefer light themes and many that prefer dark. It's best to have both due to differing opinion. The MyBB theme I am currently designing makes use of jQuery in such a way that it will allow you to switch between dark and light versions of the same theme.
For myself, however, I take preference with light themes.
Personally, I like them both. I like dark themes because they are easier on the eyes at night, and light themes because they look better both on mobile and screen. What I really like is a mix between dark and light.
I prefer dark themes myself, but sometimes it does depend on the niche and what 'suits' the board more. I like having an option though. I have a Walking Dead forum and I started with a dark theme, but I've also added a light and a medium theme that still relate to TWD.
Additionally, I'd say that halloween styles should probably be in dark colours, whereas ones for new year, christmas or other seasons should be in lighter colours.
I'm personally a fan of dark themes. Easier on my eyes browsing in dark environment with proper color contrast that doesn't hurt eyes too much. But at times I also prefer light colors, haha. I love it most when a forum or website has theme chooser so I can change the theme according to my mood. XD