My terminal background keep changing after each restart
I suspect that you are using the profile named Solid Colors in Terminal.  Each time the terminal opens, it cycles to a random background within /Library/Desktop\ Pictures/Solid\ Colors/ folder.  If you press Command-i, the inspector will open and you can change the settings of your current window.

Try clicking to "Pro" and then back to "Solid Colors" a few times.  You should get different a effect from Solid Colors nearly every time you come back to it.

I believe that you will have to make a new settings profile with the background color you want and then set that profile as the default.