You do have some colour choices with the uniforms, if you want to portray two separate scenes, illustrating the change in the uniform.
Early war they were pike grey, while field grey began to be introduced during the autumn of 1915. Initially they were cut the same, but soon gave way to simpler stand and fall collar. Helmets began to make an appearance during the latter half of 1916. There was also changes to insignia ...
regards,
Jack