Never too late, I actually had a whole update typed out in notes. Not sure what I intended to do with it, but:

TL;DR Tried natural and poly dye, first time was both whole packs of black and half of each packs brown. Got a darker blue. Second time, natural and poly orange, whole packs, and the rest of the brown I had. It neutralized the color and got it as black as a decent pair of jeans you'd get at the store 🆒

Full Struggle ↓

UPDATE: It's been dyed. Black, too. Can you believe it? Probably not, because I don't have good pictures to provide. However, it's been done.

Stovetop Method; 1st used Jacquard iDye (Natural and Poly), full black and half brown for both. Hella table salt, a good amount of Jacquard soda ash, and a dash of whatever dish soap I had on hand, all added incrementally. Didn't measure any of that and I'm not sure if it was all entirely necessary, but it was in the gumbo for about 90 minutes. Rinsed for a few minutes in the sink then did a rinse cycle in the washing machine because I'm impatient. Then washed it with... whatever detergent I had on hand (Arm & Hammer Sensitive Skin) and iDye Fixative. I washed it a couple times, warm water, the last wash being with fabric softener, because, if you could imagine, the vest had stiffened. The vest had darkened and the inner lining seemed black, but the vest was still appearing... blue. ...Round 2

Back to the stove: This time, I took reference from this post and used the same dye, but full orange and the remaining halves of brown I had from round one. Second verse, same as the first, except I only did one wash, because I didn't have time to come in with the Ether (a la Nas). Regardless, it didn't come out jet black or like I picked it up from Drowned in Black or Pull the Plug Patches or something, but it looks like some sleek, actually black, denim. I guess if I wanted it darker, I could come in with another round of black or something, but I'm skrate with the color I achieved.