Here is a cool theme pack I was using last month for my Ubuntu desktop. The theme color for this customization is green. So, I have included a green login screen, a green theme, and a green icon pack with a green wallpaper.
This Wallpaper is from Deviantart :
The download page goes here : Here.
The theme is named “Aqua Dreams.”
Get the theme Aqua Dreams : here.
An excellent login manager theme to go with this theme.
The link is : Leaf Gnome.
Icon Pack :
Icon pack lets you change all system and GDM icons.
The Icon Pack is from this website.
That is all the way to going green. Do not forget to share your desktops, screenshots.