Why are colour prints so much more expensive than black and white ?

I think the different in ink's price make the unequal in pr inting. And the higher price of producing colour inks make it more expensive. In arting, you are easy to have black or white colour. But if you want to have other colour, you must mix it together. For example, if you want to make green, you will have to mis yellow and blue, or to make purpil, you will mix blue and red. One more reason that i think it makes the price of ink colour more expensive is that, the supply of ink colour is much more less than black and white. In a paper, more than 80 percent is for black and white, and the rest of it is other colours. So you can finished a bottle of black ink in a week, but you might not finish bottles of different colour in a month (except you use other colour to text, not black) :)