it would be nice to be able able to change the background colors of the export file, since it's gray it use a lot more ink that it should, even more when we print 60+ pages of stocks.
Currently, the only way would be with some custom coding. Mainly CSS. I'm sorry.
I'm also wondering regarding another issue, for some reasons pictures when i export stock are randomly removed, anyone know why that could happen
When I saw this happening was because the PDF generator library was not able to access the image.
You can check if you can access the thumbnail URL externally. By pasting its direct URL on a browser.
And if you have your site protected through an htaccess password, this can cause this issue too. But in your case, I guess that is not what is happening because all of them would be missing (not only some).