I had a similar dyeing adventure you are having but with patience i did hit the soot black. i bounced around a few times before i got lucky. The last few jumps were torture as i was so close. i went midnight blue -> deepwood green -> void blue -> deepwood green -> kobold brown -> sootblack



Remember its not an exact science and patience is your friend
Don't overfeed, when you are in those color ranges you are so close you want to take baby steps

My last two steps:
i was at deepwood green and i fed one(1) pineapple and one(1) valfruit. rng wasnt with me and i ended up with Kobold brown. from there i fed one(1) plum. the rng gods took pity upon me and i got soot black.


Good luck!