I'm gonna go a little more in-depth on alternate Blue and Red versions of certain nations that I'd like to see in BAT. It's a quality of life improvement more than anything.
IJA and IJN (Red)
Japan was a member of the Allied Powers during WWI, capturing Tsingtao and several Pacific islands from the German Empire. They were also a major participant in the Allied Intervention in the Russian Civil War. This is already adequate reasoning for the red versions' inclusion, but another possibility is an alternate history where the Axis won WWII, pitting Japan and Germany against each other in another 1946-style scenario.
Red Army (Blue)
Granted, having the Red Army on the blue side seems strange in appearance, but it makes sense in function. The Red Army would represent two things: the fledgling communist regime during the Russian Civil War and Allied Intervention, and the Soviet Union in 1939 during the invasion of Poland.
Turkey (Red)
A relatively ambiguous addition. The final stages of WWI saw the very brief entry of the Red Army against the Ottoman Empire. Less historically, this addition would also facilitate an alternate history in which the Central Powers won WWI, seeing Europe turn against the Ottoman Empire in a new war for control of the Middle East and North Africa.