How do I change desktop background with a terminal command?

I trying to add to my OS X configuration script a command which sets the background to the plain dark grey, however, when applied, it only sets it to the main monitor and any additional monitors currently connected keep their current background and any added thereafter still receive the default space background. What I have so far is as follows: # Change Desktop default BackgroundColor to grey defaults write com.apple.desktop '{ Background = { default = {BackgroundColor = ( "0.2549019753932953", "0.4117647111415863", "0.6666666865348816" ); Change = Never; ChangePath = "/Library/Desktop Pictures/Solid Colors"; ChangeTime = 1800; DrawBackgroundColor = 1; ImageFileAlias = ; ImageFilePath = "/Library/Desktop Pictures/Solid Colors/Solid Gray Dark.png"; NewChangePath = "/Library/Desktop Pictures/Solid Colors"; NewImageFilePath = "/Library/Desktop Pictures/Solid Colors/Solid Gray Dark.png"; NoImage = 0; Placement = Crop; Random = 0; }; }; }' How do I set the default the the dark grey background via a terminal command? How do I change all monitors already configured to grey via a terminal command?