I can't say enough about the healing benefits of honey. Since you're already onboard with herbal treatments, raw local honey would be an affordable way to carry this wound all the way through to complete healing.
I knew nothing about deadened black skin when I treated my rooster who was attacked by a coyote five weeks ago and only trimmed torn flaps of gummed up skin to tidy the wound, not because of any harm it could bring him. I coated his numerous deep wounds, including a body cavity puncture, with honey, and by the end of the next day I could see signs of healing.
The wounds widened as the skin began to heal. The pulling back was alarming, but the honey prevented infection, and gradually scabbing began to form and new tissue started filling in and closing the wounds. The skin discoloration was alarming, but I was assured it was probably just bruising, and sure enough that's exactly what it was.
You mentioned a saline solution. Do you have epsom salts? A warm bath or flooding the wound with an epsom salt solution daily will partner well with the honey. I didn't do any bandaging and left the wounds exposed, and no stitching. Honey is sticky and not so fun with feathers, but it's water soluble and easily washes off in a bath.
I've documented my experience in a discussion here if you'd like to learn more. I used Manuka honey, but I've seen research and other healing successes where raw honey was used, which is much more affordable.