A green mountain without ink is not an idiom. is the title of a contemporary TV series.
There is no ink on the green hills - there is no pen or ink on the green hills. In other words, the green mountains are not painted with pen and ink.
The words come from a poem by an unknown poet in the Ming Dynasty: Green mountains are like paintings without ink for thousands of years, and green waters are like stringless harps for thousands of years. It means: Although the green mountains have never been painted, it is a beautiful picture that has been preserved for thousands of years; although the clear water has no strings, it has played the melodious and melodious sound of the piano from ancient times to the present.
(Or translated as: The green mountains are a picture that although there is no pen and ink, can last for thousands of years; the green water is a melodious guqin that although there are no strings, it can sound for thousands of years)