I am working on a Polish army after taking part in this game -
http://www.wfgamers.org.uk/resources/im ... ffield.htm
I am asked about the infantry and you can forget the 'Polish Guard' unit. This is a unit of the Saxon army - like the Swiss Guards or Irish units in the French army. The real Polish guard is called the Gwardii Krolewski.
On uniforms basically no one knows what the Polish infantry looked like. They could of been wearing 'Eastern' style uniforms like on the page linked to above -
http://www.wfgamers.org.uk/resources/C18/faq.htm. The Russians were wearing similar styled uniforms until at least 1703.
Some of them might be wearing green or red but that doesn't seem to be certain. After the GNW was over the army was 'reformed' and they were in red coats like the Saxons.
As already mentioned Polish infantry was pretty rare. Often there were none in the armies and the most in one army was 3 small units.
I hope this helps