I'd prefer to knock a hole in the wall and run the in the wall for that purpose instead of on the wall with a cover. Realistically though most of those wall covers are made with paintable plastics so that you can paint then to match your walls.
Pure black though could almost just get away with a piece of ABS and split it in half.
Use a swiffer duster for light cleaning, as long as your not scrubbing you're not going to scratch the monitors. A datavac to blow out any vents is a good idea. Monitor spray and microfiber if it's really bad.
As for cables...
If you can't run the cable through the walls, there's a few options;
Use cable tray/raceway. Legrand is the best known and they have several types of various materials. The basic plastic raceway will have a mild adhesive on the back and can be painted. You'll see their 'cordmate' lineup in the electrical sections of your average homestore
Legrand Non-metallic site
Your other option is to run the cables through piping that's attached to the wall. I'd for DVI cables you're probably going to need 1-1/2" or 2" due to the chonky connectors. PVC/CPVC will probably be the cheapest that won't look completely awful. Black metallic piping will also work if you want an 'industrial' look. Both can be readily painted, though you'll need a good primer and some basic surface prep to get the paint to stick well.
Something like this maybe?
Black Latching Cable Raceway
Black Latching Cable Raceway is a sleek variation from the standard white paintable raceways, ideal for installation on desks or office tables, Shop now.www.cabletiesandmore.ca
There's a 2 1/2" wide version, but it looks like it's only in white.
Kable Kontrol® Hinged Lid Cable Raceway | Wall Cord Covers
hinged lid wall cable raceways are designed to protect and conceal wires and cables that are being run along walls and baseboards inside your home. Shop Now.www.cabletiesandmore.ca
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