Why any manga must be black and white?

Question:It doesn't have to be black and white, in fact there are plenty of graphic novels that are in color, but here is why most are not.

The majority of manga artists choose B&W because it is easier to draw and thus they can release new volumes at a faster rate.

From the perspective of a publisher, it is much cheaper to publish B&W than it is in color.

Time is money, and money makes the world go round.

Best Answer - Chosen by Asker: It doesn't have to be black and white, in fact there are plenty of graphic novels that are in color, but here is why most are not.

The majority of manga artists choose B&W because it is easier to draw and thus they can release new volumes at a faster rate.

From the perspective of a publisher, it is much cheaper to publish B&W than it is in color.

Time is money, and money makes the world go round.

Therefore more ink will be saved.

it takes to much time to get all the shadowing right

Since manga artists have alot of pages to draw, I'm assuming it would be a pain to color in everything.
Plus, you'd only have to use black ink for the printing.