In logcat I am getting an error which is thrown from the Chromium source.
W/AwContents﹕ nativeOnDraw failed; clearing to background color.
In my case, in Android 4.4, I was getting a black background no matter I set what and this error message in my LogCat: nativeOnDraw failed; clearing to background color.
From Googling, it seems to be because hardware accelerated canvas rendering is not supported in Chromium WebView. I added this line to the WebView to turn off hardware accelerated canvas and now it works.