but it does not work. The posts under the category do not take the page header but still keep the theme’s global template, though I have purged the cache and cleared the web browser.
Perhaps, the reason is that one post/page often has more than one categories. Or, one category is used for more than one groups of posts. That means there is some sort of overlap among categories and posts. So, if I add a page header to a category, it does not mean that all posts under that category will take that page header, because the posts are also under other categories to which other page headers or the default template are assigned.
Is that correct? And what can I do to practically add a page header to a category and make it work for the posts under that category.
Please have a look at the post from the link provided below. I have assigned a full screen page header to the category of the post (the post has more than one categories). But the post does not take that header. The only way I can do it is assign the page header in the Edit page of each individual post, which is time consuming as I have a lot of posts under several categories. And it will also time consuming if I would want to change the page header again in the future.
Hope this is clear to you and you can find some way for me to make it work and in a faster way.
that method assigns the page header to the Archive page, not the single posts within. With Page Headers there is not a way to achieve this.
However, GPP 1.7 is about to be released in Beta and the new Elements module which replaces Page Headers and Hooks will allow you to set Display Locations including Posts by Category.