As mentioned in 6299405, we still have a non-empty finalize() method in
IndexColorModel. It would be fairly trivial to remove this method and replace it
with a more prompt mechanism, specifically the Java2D Disposer thread. This may
help reduce overhead in creating and disposing small indexed images.

Another minor point: ColorModel has an empty finalize() method. I'm not sure why
we can't just remove that method altogether (it would not be considered an incompatible
spec change since it's just overriding an existing method on Object).