I've used bbq hardwood charcoal, many times for this, but only on a fun hobby level.
If the colors aren't what you are used to, I am going to say more grays and maybe black splotches. Maybe, possibly there is residual unburned wood in the charcoal, especially if it smokes some when lit for grilling. I have done the quick hardware cloth sift of the broken up charcoal, then load it up in a big old cast iron pot and heat it for a little bit in a fire pit, with a cover on. I don't think it should be burned in open air, down to ash, just heated and only if needed.
Only thoughts, hope you can work around the supply problem.