Re: Superficial question...
I used to have this program called Ultramon which easily allowed me to have a different background for each display. It's $40 which is hefty if that's all you want to do. I'm sure there are free alternatives out there.
FX-8350 @ 4.7 cooled by H80, 32GB Mushkin Enhanced Blackline 2133, Asus Sabertooth 990FX, 2x Radeon HD 7850 2GB in X-fire, 500GB Samsung 850 Evo, 4TB Seagate, 3TB WD Black, 2x 1TB WD RED in RAID 0