Every player on the team has a different variation of the blue, white, black, and the green on their shoes. Some have green around the ankles and some just on the soles, and everything in between.
Marshawn was fined not because of the green upper, but for the solid GOLD cleats and bottoms of the shoes he wore against the Texans.
Idiots need to get their facts straight.
Edit:
An exhaustive search of the interwebs produces the same story. Not a peep about the gold anywhere, but that is the color that differs from the Seahawks scheme, not the neon green. Too funny.
Look at the color of both Zach Miller's and Russell Wilson's shoes in this gif:
Same color green as on Marshawn's shoes. Did they get fined? Nope.