Non-opaque AWT frames don't get their paint() method called so
there's no easy way paint after the initial show.

calling repaint() doesn't help - the paint() method doesn't
get called. Getting frame's Graphics and rendering to the window
directly doesn't work either.

Run attached test, create non-opaque frame:
  java -Dusenonop TSFrame
Or run
  java TranslucentShapedFrameTest
and check non-opaque, create window

It is supposed to be animating (changing the colors of the gradient).

That doesn't happen. If you put a printout into the
Frame's paint() method you will see that it's not getting called.