Different header for different category?

I’d like to have a different header for posts in different categories, for example, say I post something in the category “Economy”, then I’d like to it to display a flash header I’ve made which says “Sailormarcus’ blog – Economy”. I’d also like that header to appear if you go to the “Economics”-category list of all posts, naturally.

So, how would you go about doing this? Any answer will be much appreciated!