My cousins are all police officers, all of us look identical, plus we're all named Jenny."
Officer Jenny about her family
Officer Jenny (Japanese: ジュンサーJunsar) is a police officer who lives in every city. They can be told apart by Brock. She uses Growlithes and Arcanines as police dogs.
Their Japanese voice actress is Chinami Nishimuraand in English she is voiced by Lee Quick (Seasons 1-6), Jamie Davyous Owens (Seasons 7-8), Emily Williams (Season 9-13), Jamie Peacock (Mastermind of Mirage Pokémon) and Emily Jenness (Present). Originally they had blue hair until "Here's Looking At You Elekid" when the animation changed to digital effects changing their hair green.
The Japanese name, Junsar, means "police officer". The Jenny officers often accompanied by Growlithe, to use as a police dog (although there are exceptions, like one had a HoennSpinarak or where another has a Meganium, Parasect and Tangela or one that has the Squirtle squad, etc.). There are some other minor differences between each of them, but not many as the Joys. The only differences are the symbols in their caps and uniforms (which are different depending on your region). Unova Region Jennies have the back of their hair and their bangs cut.
The Jenny Family all appear identical as a parody to how character models were recycled and reused in the first Pokémon games. This also applies with Nurse Joy and Don George.
When Duplica imitated Jenny, her hair looked more like the current color than the one back then.