Thread:Extension talk:Flow/Appearance/reply

I'm not sure what you're saying, posts in the Flow prototype have white backgrounds and no borders. That page has pointers to better places to give feedback on the design; this Extension: page is more for help getting the PHP working. Thanks for your interest.

(Maybe you're referring to the gray background to comments on this page? Some talk namespaces on mediawiki.org use Liquid Threads, a different discussion system.)