While DC's Green Lantern once had the dumbest weakness where his ring wouldn't work against the color yellow, it was eventually retconned and largely forgotten, however, Iron Man actually made the weakness to color not as ridiculous. During a battle with Marvel's version of Green Lantern known as Doctor Spectrum, the Armored Avenger unleashed a color-based attack that was far more logical in comparison.
Remarkably, Green Lantern's power ring used to simply shut down in the face of the color yellow, being ineffective against everything from lemons, rubber ducks, to anything simply painted yellow. Eventually, this bizarre weakness was retconned by DC writer Geoff Johns who revealed that the fear entity Parallax was responsible for the «yellow impurity» found within Green Lantern rings. Parallax had apparently been imprisoned by the Guardians of Oa within the Green Lanterns' Central Power Battery, resulting in the yellow color of fear becoming a weakness with Lanterns constantly needing to charge their rings from the Power Battery. Once Parallax was released, the yellow impurity became something the individual Green Lanterns could overcome.
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However, the retcon explanation doesn't change the fact that the weakness to color was infamously dumb and very strange, one that Marvel Comics improved upon when Iron Man fought Doctor Spectrum in 1963's Avengers #70 from Roy Thomas and Sal Buscema. Wielding his prism of power, Doctor Spectrum is very clearly Marvel's version of Green Lantern, often fighting alongside Hyperion (Superman), Nighthawk (Batman), and The Blur (Flash). However, when Doctor Spectrum and Tony Stark went one-on-one, Iron Man fired a blast of ultraviolet
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