Color Variant On US Scott 221 (4 Cent Trans Mississippi)

Does anyone know if the top stamp (of the 4Cent, Scott 221) is a variant or what might have caused the color of the top more brown hued stamp (compared to typical orange, below)?

Welcome to the forum.
Your stamp is called a 'color changeling'. Although it is sometimes said to be oxidation a better description is sulfurization. Basically there has been a sulfur chemical environmental reaction causing the stamp to change color to what you see.

You can bring your used stamp back to more of it's original color with a short bath in 3% Solution of Hydrogen Peroxide. You can find more details on Stamp Smarter website, under the How To section entitled "How To Remove Oxidation". You can also search this forum for 'Oxidation' to learn more.
Don

Thanks. Never knew this to occur. I'll probably leave it as is, as it's value is not that much and I find it more interesting as an example of a color changeling.