There is a TV show by this name. And I heard someone saying it too. I googled its meaning but the effort went in vain.
something is the new something else
is a way of expressing a changeover when talking about a common property or characteristic of the two somethings.
grey is the new black
refers to the change in fashionable colour choice, originally black was very popular and de rigour, but for the new season the new colour is grey
Orange is the new black
Orange Is The New Black (OITNB)
Is the title of an American TV show and a pun of sorts. In the storyline a public relations (PR) executive is sentenced to prison. Often PR executives may wear corporate dress which is muted and of a dark colour, usually black or near black, a nod to stylish marketing. In prison, inmate dress has been striped uniforms to make the prisoners distinctive. However, nowadays, prisoners will wear high visibility clothing so they will be easier to spot. Orange is used extensively in the US penal system, for example Guantanamo Bay. So the title is describing the transition of the main character, Piper Chapman, from corporate workplace to prison cell.
The title may also be a reference to a (hoped for) change in sitcoms styles by the producers. Previously there were sitcoms based in the fashion industry, i.e. Ugly Betty, where the predominant colour of choice was black, i.e. the little black dress (LBD). The colour being associated with OITNB is prison orange. The title would signify that OITNB would (like to) be replacing other sitcoms in the ratings.
Because of the popularity of the show, the use of orange has become more fashionable (the Dutch will appreciate this) causing some prisons to change inmate dress back from orange to stripes.