Solid, warm colors allow me to id the pc (yeah, KVM with 3/4 ports connected...), and quickly find what I need.
Getting rid of the standard issue wallpaper is one of the first things I do.
YMMV.
Me, too. Very first thing I do is set up a light blue or light turquoise desktop. Then, on Win 7, I get rid of the damned Aeropeek.