Xcode editor background color change

How can I change the background color of xcode editor from white that is now to some other color?
Thank you very much!

Xcode > Preferences > Fonts & Colors.

I tried to change it from there but I couldn't.
Am I doing something wrong?

I'll assume that you're clicking in the wrong position (I don't blame you). You have to double click in the colour column.

I double clicked it but the I get a strange message about the necessity of doing a copy because this color is owned by the system.
Any ideas what should I do there?

The message you're getting is a warning about changing the default colour theme. If you notice, there are various colour themes. Select "Make Copy" and then edit to your heart's content.

Ok it worked.Thanks for your help and your patience!