Assign a new theme to Zero App, with different colors

I have a small problem:
I created a Zero App on my website. I also created a new theme.
I want the Zero App theme to have different colors than the main theme.
In the Zero App settings, I assigned the new theme.
If I change the colors of the header, footer and background in the Single Post layout, it changes on all pages of the site and not just on the Zero App pages.

How should I do?
Thank you.
Nuno F.

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