I'm having an issue with my desktop as the title eludes to. I recently found a background I like and I prefer to have it centered. This leaves some room for default background (blue) to cover the top and bottom of the screen.
The problem ensues after adjusting the default color to black. The Display Properties box will remain white, as pictured. It will only disappear after I click the "X" and it will prompt me to End Program. The text mentions something about Rundll32.exe and the subsequent "Send Error Report" message mentions "Dll as an App."
After encountering the error my desktop picture will remain, but the color will revert to blue after I restart or boot up my computer at another time. Also, I had accidentally enabled the Language Toolbar on my taskbar and now it will be re-enabled upon startups.
In addition to this, sometimes my computer will fail to properly boot up at all. The screen will stay black and I will have to physically turn it off. After the first failed bootup, I get the "Safe Mode/Normal startup" screen and the computer will boot up properly in normal mode. I don't know what else the rundll32.exe controls, but this seems to be the heart of the issue. Any suggestions or ideas would be appreciated.

Looks like you have an aftermarket theme that could be causing the issue. Go back to a built-in Windows theme for a few days and see if that resolves the booting issue. Also, you may want to download and run Malwarebytes Antimalware. A lot of themes have nasties packed inside.