Category template issue

Hello,

I have a template category on my blog, with child categories, blue, red, green and so on under the template category.

I would like to create a category template that will be used whether you are on the parent theme category or one of it’s child categories. I’ve tried using category-template.php, but that will not work for the child categories.

How should I go about achieving this? Is it possible with a custom categories template, a custom post type and custom taxonomy, or something else? I am open to suggestion, but what I don’t want to do is create a desperate template file for each on of my categories. I would like to keep it as DRY as possible.

Any suggestions or advice would appreciated.

Thanks