Hello @sportetassocies
Hope all os well, regarding the first issue, where the popup shows u on all pages, despite the settings “Only these pages”. So far I see the popup is showing up only on one test page that you’ve created here /test-for-hustle/. If you found a plugin that was conflicting with the Hustle, please let us know.
On the homepage the background of the text has the right color but inside an article, the background becomes grey.
If I understood correctly, you mean the grey background color behind the main content. Please see the screenshot:
https://take.ms/kKMab
Please, edit a popup, go to the Design section, enable “Customize colors” option and change the color of Main Background to a color of your choice

If this will not work, please add this CSS code to the Appearance > Customize > Additional CSS:
.hustle-modal-content, article {
background-color: #b03e34 !important;
}
Plus i discover a responsive issue (maybe it’s my theme). On mobile, the image is cropped and you can see only one sentence of my text (with no indication to scroll).
The scroll option for the content inside the popup can be done only within this section. Please see the screencasts:
https://take.ms/Hp1as
As for the image, since teh design option is selected for your popup is Cover, it responsively crops the image based on the mobile device dimension to fit the image in an image container.
You can change these setting sin Design section, under Featured image fitting, change the image alignment in Horizontal image position and Vertical image position.

Change the Vertical Image Position to Top, for an example, this way the image will not be cut at the top in mobile view.
Hope this helps!
Cheers,
Nastia