Color Blindness, Red-Green (3.5e Trait)
From D&D Wiki
Red-Green Color Blindness
Your color vision is just not quite right when it comes to red and green.
Prerequisite: Normal vision
Benefit: Spells that rely on color (dancing lights, scintillating pattern, etc) to disorient work at half efficiency.
Drawback: You are unable to differentiate between red and green.
Roleplaying Ideas: "Why is that green dragon breathing fire? I thought they breathed poisonous gas..."