Guild Wars 2

Black dye on transmuted armour automatically dyes it to the default dye remover colour. All other dyes work normally.

Confirmed with both my engineer and mesmer.

I am having the same issue. I transmuted some exotic nightmare heavy armor. Now when I try to add black dye to it, it becomes “dye remover” when the window is closed. All other colors work.
there are now a few forums for this

https://forum-en.gw2archive.eu/forum/support/bugs/Dye-Remover-I-can-t-dye-my-armor

https://forum-en.gw2archive.eu/forum/support/bugs/Dye-Remover-bug/first#post1091275

https://forum-en.gw2archive.eu/forum/support/bugs/Heavy-Nightmare-Armor-and-Black-Dye/first#post438617