Why does my dumpling /dimsum/momos turn dark brown while steaming?
Based on the color, it looks like your dumplings might be exposed to too high a heat on a surface that could actually sear them (that metal pan for example). It also looks like those dumplings might be overcrowded and being handled too much so that they'd break.
If it's possible, I'd see what your clients are doing to prepare the dumplings you send them and make sure it's not an issue with their technique.