Borders turn bright when mai ncolor goes below a lightness threshold

Hi, i’m trying to make the theme dark greenish, but if i go below a lightness of 30, i get bright borders everywhere. Why does that happen or how can i change the border color

Hi - I don’t know much about custom theming approaches, so please forgive the possibly silly question - what tool are you using to create that theme? Tagging that in here might help folks familiar with that tool identify this post and contribute their knowledge.

plasma color setting