Georeferencing PNG with transparency via gdal produce "green pixels" in QGIS?

This is just intriguing while not blocking my way, but I wonder what is going on and would like to get feedbacks from more experienced users.

1) Given a png files (1.1MB) such :

2) I restore georeferencing using :

gdal_translate -a_ullr 67.0 37.5 99.0 27.0 -co COMPRESS=LZW  -co ALPHA=YES       ./trans.png ./trans.gis.tif

3) The output (1.6MB) is :

4) Loading it in Quantum GIS, it get well positionned (georeferencing works!), but the image is ill colored with the darkest areas (and only them!) becoming green :

Is this green artifact normal ? How to fix it (so I may see the expected black pixels) ?