Sandor,
If you would like to paint Napoleonics (and who doesn't!), far and away the best uniform source are the Rousselot plates. The plates are now sadly out of print, however Andrea Miniatures a few years ago published a book with all the Napoleonic uniform plates within. This book will cover almost every question you may have.
Bear in mind that during the retreat, uniforms quickly became tattered and essentially looked nothing like the figure would look in full dress. On top of this, the retreating army used blankets, sheets, and anything else they could scrounge to help protect themselves from the elements. You're pretty much free to use artistic license to paint any blankets, etc on the figures, but I would at the least, stick with the actual uniform color of the soldiers themselves, painted suitably soiled with mud/dirt and weathered accordingly.
