Right now i'm using the Google Shopping app which is obviously limited. All my product images on my site have dark backgrounds, for Shopping you should use a white background. So I'm wondering how do I keep the dark backgrounds on my site but use the white backgrounds for Google Shopping. Is there an app that you know will do that?
1) You need to find a solution that allows you to upload or edit the images in the feed itself. This in most cases is a data feed management tool
2) You can create a spreadsheet with as a supplement feed to overwrite Google Content API data. More info: https://support.google.com/merchants/answer/7439058?hl=en
Make sure you are able to host your images somewhere on a public server.
Alternatively, if both options do not fit your needs, consider changing the images in your Shopify account.
Hope this helps.
Are your images saved with a transparent background? As in, is the dark background a result of the actual website being dark or are the images saved that way? If it's the former, it shouldn't be too hard to adjust that. I've never used the Google Shopping app, but typically images with a transparent background show up as the image + the white background. If that doesn't work, you can easily add a white background yourself.
If you've got graphic design experience, you could use the lasso tool if the image is already part of a specific background. However, this could turn out looking... not so great.
Pardon if I misunderstood the question!