Hi, the only real way to change this, but still have the color chooser in the backend is to modify the styledeclaration.php file.
If you haven't used this yet, grab it from the libraries -> gantry -> features -> styledeclaration.php and copy it into the features folder in your gantry template directory - if there is no features folder there, create it and put the file inside. This way you can override it without changing the core files.
Once you have that copied over and open, you'll see this where the color choosers are applied via CSS. Find a line that looks like this:$css = 'body {background:'.$gantry->get('bgcolor').';}';
Just change background to background-color and you're all set. This is also how you can add or remove elements that are controlled by the color changers. Hope that helps.