Chicago-style relish is a type of sweet

pickle relish A relish is a cooked and pickled product made of chopped vegetables, fruits or herbs and is a food item typically used as a condiment to enhance a staple. Examples are chutneys and the North American relish, a pickled cucumber jam eaten with h ...

typically used on Chicago-style hot dogs.Zeldes, Leah (July 20, 2010)
"Origins of Neon Relish and Other Chicago Hot Dog Conundrums"
, ''Dining Chicago''. Retrieved July 19, 2016. The unique color of the relish, often referred to as "neon green", is created by adding blue dye to regular pickle relish. The first use of Chicago-style relish on a hot dog has been attributed to several different restaurants, including

Fluky's Fluky's is a Chicago-area fast food restaurant and mail-order food purveyor known for hot dogs."Fluky's History"

and

Superdawg Superdawg is a drive-in hot dog stand with carhop service. It is located in the Norwood Park neighborhood of Chicago, at the intersection of Milwaukee, Devon, and Nagle Avenues. Superdawg has the distinction of being one of the few original drive ...

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