Ugh...the dreaded grey sausage. Been there done that. I noticed that I got grey sausage whenever my fire was too hot (im talking fire temp, independent of cook-chamber temps). Super hot wood fires in my offset tends to make very thin black/grey soot which will ruin the appearance of anything but pork butts and brisket. I’m sure it doesnt help the flavor either.
..
The following advice might depend on the type of fuel and cooker to some degree....but grey sausages (and chicken) might be best avoided by making sure the fire is on the calm side. Symptoms of a fire that is too hot are roaring bright yellow flames, and/or if you notice backflash when opening the firebox door.
Before you put on the sausages, you should make sure the fire is well established, calm, and making most of it’s heat from embers (not flames). And avoid adding fresh splits while the sausage is cooking.
As far as salvaging greyed sausage, Im not sure. I’d be inclined to wipe off the grey soot, but not sure it would help any.