I think you are right Mark, excluding the Tartan Army, British Uniforms are pretty boring and you probably only need about a 5 colour Palette to paint them all. Most other countries have more colour variety in their uniforms as opposed to distinction by Number. Although Prussians are Blue, Swiss are Red, Austrians are White, Russians Green etc, there is tremendous variety within the uniforms of these countries which makes them more interesting than the British Regiments.
I'm not a uniform expert so this is just my very broad brush opinion, I'm sure plenty out there will disagree with me.
Keith