FULL PRODUCT VERSION :
java version "1.5.0_09"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_09-b03)
Java HotSpot(TM) Client VM (build 1.5.0_09-b03, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
PNGImageWriter always sets the bKGD chunk as grayscale because it sets each channel as the value of the red channel. Here is the code segment:

int chunkRed = metadata.bKGD_red;
int chunkGreen = metadata.bKGD_red;
int chunkBlue = metadata.bKGD_red;

I made a copy of the classes used and changed these lines to set the colors properly and it behaved as expected.


REPRODUCIBILITY :
This bug can be reproduced always.