At last I've had success with the bif thanks to your instructions Rythmic: cover the places black dots appear with the background colour (a brown parchment colour). I don't get good results with the lbm for the moment.

The Purpgrab CA program intrigues me because when a Tga is dragged into it you can obtain not only a bif but also a lbm. It's easy think CA guys use this program to obtain the lbm and bif unit icons in a quick way. However I only get strange bifs and lbms with black as background colour instead of light grey.