Why is new a layout created, every time I click on the layout templates?
At the pictures of the different layouts templates, you can select one of the templates as a 'new' layout. Once you click on a template, a new layout is created. After selecting, it appears in the list of existing layouts. To edit your layout template later, select it from the list.
Hint: Give your layout a unique title to find it in the list. Why does change the color of the button only partially?
This is probably, because special codes for the button are stored in the CSS editor which controls the color. If you like the button in the current style, you can fully customize the color, only in the CSS editor.
Here at the help center at the topics 'colors and color codes' and 'CSS Editor' you will find an explanation of how you can change the color.