As of today’s (April 19th) update, the old dye preview bug has resurfaced for me. I’ve spoken to several players in-game with the same issue. The old thread is linked below.
https://forum-en.gw2archive.eu/forum/support/bugs/Hero-Panel-Dye-Preview-Failing-merged/first
Dyes are applied correctly outside of the Hero panel; in the Hero panel, however, dyes may not show up when hovering over a color swatch. If they do show up, they occasionally get stuck, i.e. they will remain displayed even when moving the cursor off of the corresponding color swatch.
Hopefully this gets some attention and a speedy fix.