Mary: Just released version 24.6 which addresses this specific issue.
Somehow Firefox doesn't color new blank tabs when they are opened at random or under load conditions.
As to your specific issue, the "." doesn't match tab that are blank and do not have any domain loaded. For that you should create a preference "about:newtab" and it should match the new tabs. Please let me know if you still have issues. Pls also attach the options screen of domain preferences as well as a screenshot of Firefox.