If you take a look at Template Hierarchy category-news.php would be archive template, that is for a list of multiple posts having specific category.
There is no such thing as template for individual post, having specific category, in native template hierarchy.
There are different ways to handle such, depending on your needs. Typical are:
- styling it via CSS (WP tends to output a lot of useful body classes to use)
- handling markup conditionally inside template file
- adding your own template file logic to native hierarchy