You can't easily make the background color match the web page. You'd think that Applet.setBackground() would just Do the Right Thing.
This is also applicable to Swing; you can't set a background color on a parent component and have it propagate to descendants. The first non-opaque component you run into is going to get its background from the UIManager. I really don't want to have to figure out which UIManager colors I have to override just to set the bloody background color of my app.
Maybe the new JSR 296 will do something about this, maybe not, but it'd be nice to have something akin to the old X toolkit's resource specifiction:
The idea is that you can isolate or aggregate just about anything in the hierarchy by name or by class, and apply a resource setting to it (I guess they're calling it "injection" these days).