A red herring is an idiom meaning something that will distract or mislead. A red herring is also a herring that has been split down the middle and smoked until it has turned red. This is a long process, so during WWI, in order to economize, cleaver business people dyed the herring red. This saved on the cost of the long smoking time. Another term for this kind of red herring is kipper.
Red herring, the idiom, is attributed to William Cobbett, who in an 1807 article about the English’s supposedly mistaken report of Napoleon defeated, said that he once used a red herring to distract hounds in pursuit of a hare.
The phrase caught on and is in prolific use still today.