I am using a custom color scheme along with the Breeze dark widget style. I use Breeze-dark for GTK2 and GTK3 applications, but neither one gets applied with my custom color scheme. Instead, both GTK 2 and 3 applications use the default light-bluish breeze colors. (I am using red color theme).

This affected all versions of plasma 5 (been using since 5.1 or so), including the recently released 5.8.

Reproducible: Always

Steps to Reproduce:
1. Go to System Settings -> Colors and apply a non-default color theme
2. Go to System Settings -> ApplicationStyle -> GNOME Application Style (GTK) and choose Breeze-Dark for both GTK2 and 3
3. Open any GTK application (e.g. GIMP, Dia, Inkscape, ...)

Actual Results:  
The colors used correspond to a "Breeze Dark" color scheme, which is the default for Breeze style.

Expected Results:  
Colors should correspond to whichever color scheme is chosen in settings.