I am using the XFCE edition of Sparky, and of course it uses 'lightdm'. If you also have lightdm and like a nice GUI try 'LightDM Manager'.
Its from the developer of 'Solydxk' (the same who made our Device Driver Manager)..
Login (Users button)
Change backround/theme (Appearance button)
You can get it by 'temporarily'
adding their repo
(comment it out after install, as it may conflict with 'Sparky' repo)
deb http://packages.solydxk.com/testing/ solydxk main upstream import
I am currently sucessfully using it on 'Sparky' 3.4 XFCE.