However, GTK developers are working on a way of allowing distros to specify color schemes, so they can make apps look more consistent with the look and feel of the distro without needing to change the stylesheet. Apps will always use Adwaita, but you can optionally support color themes using a special API.
One of developers said
spoiler
don’t hold your breath on that
.
I support it. Studies have shown it has a positive impact on people.