Since you don't plan to use it for rain protection, you can abuse the tarp all you want. But wouldn't it be better to just get something that is already the right color?
If you just want a privacy screen, any unhemmed fabric will work. Or you can tape the raw ends with Duct Tape. 3-4 yards of 60" fabric is all you need for a screen that will give better coverage than the Walmart tarp.
A quick Google on "camp ripstop nylon fabric" brings up all kinda stuff. shop around and you can find it cheap. Sometimes Walmart has the cloth in their fabric/sewing section at $2/yd. Denver fabrics.com has lots at $5/yd until 7/23. Amazon has it at $5, too.