I just bought an ASUS ZenPad. I went to customize the wallpaper. Much to my surprise, I could not get a simple one color wallpaper. I was looking to have black. Addtionally, there was no apparent feature to "disable" the wallpaper. After doing some searching, I found this website: Black Solid Color Background. The website also offers other plain colors.

I was able to change the wallpaper on my tablet to black. Yeah. Of course, I need to add the admonition that what worked for me, may not work for you.