Problem with blocks on header: they won't change color accordingly to css file

Hello, I'm using the beautiful tapestry, and I've rearranged several pages with panels and minipanels and themekey also (I installed more than one tapestry on the same site and using themekey module I make some pages switch onto different tapestry layouts: in order to do that properly, I've activated the css caching in admin/settings/performance, cause IE needed a little help).

Changing blocks colors through css file always worked, but now something strange happens: If I place a custom block in header or banner region, and then try to change its colors rearranging its css sheet, nothing happens. When placed in those regions, also titles (h1,h2...) appearence won't change when I go and edit the style.css.
how could it be???
hope someone already faced this one, and knows a solution!!
thanks anyway for any kind of help you can provide! I really appreciate.