The background color for categories in beta2 is controlled by this:Style Properties
As we said in our Beta 1 announcement, we have made significant strides in integrating our CSS into the style properties system. The content of the forum list and forum view pages are now almost completely controlled by style properties.However, we would like to take this opportunity to solicit feedback on the work we have done so far. Do you think that there are now too many style properties in the Sidebar, Forum List, Discussion List, Message User Info and Message Content style property groups, or would you prefer to see a much broader set controlling a more macro level of detail?Some of these properties control fairly advanced functionality, and we would like to hear your opinion on the approach we have taken before we commit to applying the same degree of 'style propertisation' to the rest of the system.
Thanks as always. I'll create a new style to see what happens.If the background isn't changing on that palette color then it's probably due to prior style customizations like custom templates. But @secondaryLighter is the controlling color on the default beta2 style. I tested it.