Magic: The Gathering: Red magic and Blue magic. Red magic, mages, and creatures are all about passion and defiance. Blue magic tends to be big on thought and planning. Also, fire magic tends to be red, while water magic tends to be blue.
Don't forget about the flavor of the planeswalkers! The two stereotypicals of this comparison are Chandra Nalaar's pyromantic Red to Jace Belleren's mind-bending Blue. Jaya to Karn (though Karn's technically colorless), Koth to Venser, the list goes on and on.
In their childhood, the brothers Mishra and Urza fit this trope perfectly. Mishra is temperamental, emotional, and passionate, whereas Urza is scholarly, logical, and standoffish. This continues throughout the Brother's War.
Defender, the Magical Knight is the defensive counterpart to "Breaker the Magical Warrior." "Breaker's" emphasis is on his ATK and sword; "Defender's" is on his DEF and shield. "Breaker" is DARK Attribute while "Defender" is LIGHT Attribute. Their color schemes are also the opposite of each other, "Breaker's" armor is red while "Defender's" armor is blue. Their effects are also opposites of each other since "Breaker's" effect destroys Spell or Trap Cards, while "Defender's" effect protects Spellcasters (hence the names).
Nikitama and Aratama are references to the duality of god in the Shinto religion, namely Aratama & Nigitama, this card being a "evil" god, while "Nikitama" is a "kind" god, therefore they are counterparts of each other. Aratama supports destruction and anger (this may be represented by its effect that allows the player to search for a strong monster). Nigitama supports birth, growth and regeneration (this may be represented by its swarming effect and the one that allows the player to draw 1 card).
Finally, there's also the straight up examples of Red-Headed Oni and Blue-Blooded Oni.