In trisquel the file folder looks like the first picture. Debian is the second. They both use lightdm and I installed the gtk+ greeter. Unity doesn't appear to be in the debian repos but I don't think the trisquel pictures is unity (it looks fairly different from ubuntus). How do I get my debain installation looking like the first picture?
Notice the icons at the top of the folder window and the icons on the left side
You can change the icon themes by selecting the settings manager. Then, I think it's called appearance but it should be the one on the upper left hand corner. There, you can select icon themes. You can install new icon themes from apt-get, from gnome-look.org, noobslab or elsewhere like deviantart.
Download and extract the icon themes to a newly created folder named ~/.icons.
By the looks of it, the thunar example you gave me was using metacity instead of xfwm. You can install metacity with the following commands:
sudo apt-get update
sudo apt-get install metacity metacity-common metacity-themes
to use metacity:
metacity --replace
You will have to install dconf-tools and dconf-editor to change the metacity theme.
to revert back to the original xfce window manager:
xfwm --replace
