Android - after loading URL with webview can i change background color

Android - after loading URL with webview can i change background color

I have a webview and im loading an external HTML form a site. I try to
change the background color using javascript function:
function changeBGC(color){
document.bgColor = color;
}
and that does not work. but if i load locally then im able to change the
background color. Is there some kind of security inhibiting me from
changing a web page i load into the webview externally ?