I decided to create this thread, so everyone would share websites with details of colour, uniforms etc.
Ill start with the Duchy of Warsaw, the website is whole in Polish, but there are really good illustrations there,
There is a little example of what you can find - lieutenant of 4th Regiment of Foot
Spoiler
(https://www.fsegames.eu/forum/proxy.php?request=http%3A%2F%2Fnapoleon.org.pl%2Fpiechotaxw%2F4pp4.jpg&hash=13df68c0f0d31e4fec03c5013e64b4aeaaa35191)
Grenadier of 5th Regiment, along with grenadiers jacket and voltigeurs one
Spoiler
(https://www.fsegames.eu/forum/proxy.php?request=http%3A%2F%2Fnapoleon.org.pl%2Fpiechotaxw%2F5pulk.jpg&hash=8fbe6df9bcc8fcaf6cf62039742bfe28665b6c1f)
Note
All the images on this site, are based on watercolors, illustrations made by both - Polish and Foreign artists of the era
Polish Uniforms
http://www.napoleon.org.pl/index.php/biblioteka-barwy-i-broni/piechota-xw-na-podstawie-ikonografii-zrodlowej
Uniforms from battle of Waterloo
http://centjours.mont-saint-jean.com/unites.php
Spanish uniforms: Thanks to Mercuri
1 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/11/uniformes-espanoles-n-1-de-la-guerra-de.html
2 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/11/uniformes-espanoles-n-2-de-la-guerra-de.html
3 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/11/uniformes-espanoles-n-3-de-la-guerra-de.html
4 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-4-de-la-guerra-de.html
5 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-5-de-la-guerra-de.html
6 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-6-de-la-guerra-de.html
7 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-7-de-la-guerra-de.html
8 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-8-de-la-guerra-de.html
9 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-9-de-la-guerra-de.html
10 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2014/12/uniformes-espanoles-n-10-de-la-guerra.html
11 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/search/label/GUERRA%20DE%20LA%20INDEPENDENCIA%20ESPA%C3%91OLA
Peninsular Campaign:
1 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2011/08/guerra-de-la-independencia-espanola.html
2 http://miniaturasmilitaresalfonscanovas.blogspot.com.es/2011/09/guerra-de-la-independencia-espanola.html
Post other sources for skinners below :)