Feature Request: Set a Single Fill Color for Icon Backgrounds

[marcxjo]

I use a light GTK theme consisting of the usual trendy greys and blues. Random accent colors like orange for Firefox or purple for MPV just look weird and out of place. I'd like to have an option to set a single fill color that's more consistent with my theme.

No real technical argument here, just a subjective suggestion that I figure might have appeal for other folks. Happy to help however I can to get it implemented if there's interest.