If stationed overseas then uniforms would follow the pattern issued when posted, made up from local cloth and limited supplies from home, mixed with new uniforms when fresh drafts of men arrived. If newly raised then the latest pattern would be followed.
There are differences in the patterns from the WAS to the SYW, but I think most gamers are quite comfortable with figures fighting in Flanders, Germany, Scotland, the Caribbean or Canada in the same uniform, in any scale.