Adding chili powder to a dish makes it dark black

I make my own chili powder by drying (already dried) chilies in the oven till crispy. I then add them to a food processor and grind them to a rough powder.

The result is a very dark chili powder that will often darken what it is added to substantially. If I cover a steak with it the steak is blackened. Adding it to lighter soups and stews also darkens them substantially.

As you send your chili powder out to be professionally ground it likely comes out much more finely ground than my inexpensive, old, food processor. And because of that is likely to color anything you add it to more than mine.

Like @GdD said I would bet this is what is happening with your chili powder.