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Is the faint gray border appearing only around the embedded content? Or is is appearing around all elements? (Sorry, I can barely see the gray borders.) Does the gray border happen if there are no embedded images?
When you convert the SVG to PNG, are you using Save As Cairo png? The proper way to get a PNG is to use File menu > Export Bitmap. Then the background will be transparent, and should have no gray border.
Do you see any gray border when you open the PNGs in a viewer, and before you apply them to the t-shirt image? Do you see it in the SVG file? Is the t-shirt image where you see that gray border, is that still in Inkscape, or is that part done with another program?
Is the gray border showing up on the actual t-shirts, or only in the image of the t-shirt?
In your web-based "startup" is the drawing background any color except white? And all the content is 100% opaque, all the way through the process?
Sorry for all the questions. And btw, I personally don't need any monetary compensation. I just like to help

PS - So you actually have Inkscape working somewhere on a website? Is it the full program, or just the pieces that someone making a t-shirt might need? If you don't want to post the address, would you mind PMing it to me? I'm just curious
