you wrote:
So you can copy it, rename it, adjust its PHP file as well as XML file and you should have a new installable template. Note the template element (e.g. "default") is included in the PHP files class names so you'll need to adjust the PHP file.
I copied the template and renamed the copy as default_blue. I changed this in xml too. But I did not find, where in php I have to adjust. Can you show me, please?