The lockscreen does respect other settings in in the "org.gnome.desktop.background" gsettings schema, namely the primary-color key. The default is a nice bright blue and really accentuates the primarily black/dark, zoomed background images ;)
My workaround:
$ gsettings set org.gnome.desktop.background primary-color '#000000'
Some additional information:
The lockscreen does respect other settings in in the "org.gnome. desktop. background" gsettings schema, namely the primary-color key. The default is a nice bright blue and really accentuates the primarily black/dark, zoomed background images ;)
My workaround:
$ gsettings set org.gnome. desktop. background primary-color '#000000'