Here is a stupid and unimplementable idea :
From what I know ( I don't have the game ), colonial troops are built in colonies only, and normal troops on your national normal soil ( so far, am I right ? ). Say you are Mexico, if you conquer United States of Central America, will you build normal troops there, or colonial ?
Anyway, the thing is that you have a single manpower pool, which comprises all your soldier pos from your entire population, therefore you use the manpower that you gain from your colonies,
to build regular home culture troops ( so far so right ? ).
Well there should be two manpower pools, one for normal troops, the other for colonials : you can only use your homeland manpower to build your normal troops, therefore, if UK wants to have a big standing army, having a big colonial manpower pool and a low national manpower pool, well they'll have to resort on colonil troops, poping up in their colonies, of their colonies' culture, and therefore with all the risks involved ( cf 1857's mutiny in India ).
To make the distinction between normal and colonial troops would be up to the player. I mean, I think the player can grant statehood to colonies and such, therefore integrating into its offical country. This way those places would become eligible to raise normal troops. To prevent exploits, troop raising should be random inside each of the two manpower pool : if you are Austria and raise troops, you choose whether they'll be colonial or national. If you decide they are national, than they might pop up in any of your national provinces, and be of that's province culture ( be it South German, tcheck, slovaquian, hungarian and whatever else available ). This would also avoid ACW exploits : If the player raises a division, he can't know of it will be dixie from Alabama, or Yankee from Pennsylvania. that added to soldier's POP loss would make a more realistic army management, at least in terms of demographics...
I am sure that none of that is feasable, yet what do you think of these ideas ?
Cheers.