Hello, This feature is custom coding of theme and core files.

Files of css loading from our demo website, if you want to have similar features we can discuss about that as custom work.

Thank you very much.
Can you tell me if I buy it?
Thank you.

Yes i can provide description of that customization

Same to me I guess.

I wanted to make some color adjustments. But if I change the main color in the settings ("Black text"), other background colors are changed too. But that is not desired.
What other possibilities are there?

Hello,

You may change color of text for each block manually in Design & Custom Template settings

Unfortunately not. I can`t change the text or background color by set it manually in the blocktypes "promo" or "pricing table" or "slidershow". It will overruled if the "main color" is changed.