That's not a joke.
The readers want the fresh originality in the same old stories. Not even the virtue is the midpoint between two extremes sense. They don't want moderately fresh in reasonably similar stories. They want them both in full force -- although probably they don't ever get it fully in any one book, writers being only human. Something old, something new (and writing being what it is, you will probably have something borrowed in any story. Something blue is optional though.)
Then, this is not unique to the originality. Readers want your characters to be striking, individual, complex -- and coherent, recognizably unified personalities, with iconic resosance. And they want the twists in the plot to be both shockingly novel and (in hindsight) blindingly obvious. Particularly the conclusion. They want the monsters to be new and different and evoke the same horror and wonder as the old monsters. They want the magic to be strikingly odd and still recognizable as magic.
You get this trade-off down at the vocabulary level. You want your language to be clear, precise, and indicative -- and understood, which means relatively familiar. Calling a gown "cerulean" is more precise than "blue" but it does limit the audience that will understand it.
(Inspired by a thread onsartorias )