Units cards are categorized by colors:
Red = Archers
Blue = Sword soldiers
Yellow = Pike soldiers
Green = Melee cavalry
Blue green = Taisho / Daimyo
Purple = Matchlock soldiers
Grey = Siege units
Moreover each card has a mention in kanji colorized that identifies its group
Ashigaru / Ninja / Light cavalry = White
Samuraï / Ronin / Onna Bushi = Black
Monks warriors = Orange
Taisho = Yellow