I should point out that in my opinion gamers should be able to tackle their chosen period in whatever fashion they desire but it did cross my mind about the uniform aspect. Why not design uniforms using historical models for your own armies - be they set during the Wars of Napoleon or any of the other campaigns during the 19th century?
I have given this some thought on and off for some time now and have made a point of studying, for want of a better expression, military 'fashion'. In its simplest form you could say that there are three periods up to around about 1870 or thereabouts. I call these the 'tricorne' period followed by the 'shako' period and finishing with the 'kepi'. I realise that the Prussian style helmet was also influential and I would include this as following the kepi. In each case of course there would the inevitable overlap.
Whilst the tricorne was pretty much the same whichever army you served - usually the level of lace or cockades being the only difference the shako was a little less standardised. In my opinion the bell topped version was the most common type and so any troops thus attired could serve for pretty much anybody at one stage or another. Similarly with the kepi. One could also extend this to the Prussian style helmet.
My point is that for the most part figures in the requisite headgear could serve in any number of armies, regardless of national affiliation and therein lies the attraction when designing ones own forces. Selecting a suitable attired figure for the 'era' and then designing the uniform colours should be easy enough and there are certainly mainly smaller and less well known armies that could provide additional inspiration if needed. Going down this path certainly opens many avenues as one could utilise the best figures (and I mean that from the perspective of uniform styling rather than casting detail) to form ones miniature forces.
The title of this post of course refers to that staple of military maps and professional training - the concept of the blue army and the red army. These alone could provide the basis for a pair of matching opponents (and have indeed done so) with the main uniform colour of red or blue reflecting the affiliation of the force in question.
This is leading somewhere - I just have to decide where that somewhere is!