The preview in Custom Labels is a bag photo with your file on it. It is not a press proof.
Screen vs print
Phones and laptops are brighter and more saturated than ink on a bag. On-demand print is not color-managed to a Pantone chip. We do not match a hex or a brand guide swatch.
Bag color is the pouch
Kraft, black, or white is the bag, not the label stock. If your art has a white background, you will see a white rectangle on a kraft or black pouch. That is the file, not a printing error.
What we do reprint
A wrong SKU, the old approved file after you were told a new one was live, or a clearly cut-off required line — write in with the label ID# and the order. A slightly different brown or a softer black than your mockup is the print process.