Hi xgeriuz,

something is irregular on your WP or Server. This can not be a wpForo core issue. wpForo is being tested on dozens of WordPress installation and servers every day, we've never seen this issue. It seems there is a cache or security plugin which doesn't allow wpForo overwrite colors.css, something which hardening /wp-content/ folder and affects data update in css file. And this plugin may be installed on some wpForo Users WordPress's. I'd ask people who got this issue to leave a list of all active plugins. This will be very helpful.