Sapphires and rubies are both forms of the mineral corundum, but they are different colors. Why?

Thanks for your help!

Sapphires, get their blue color from iron and titanium oxides. Green sapphires are produced with cobalt, and yellow from nickle and magnesium. Pink sapphires contain tiny proportions of chromic oxide, and larger amounts produce the dark-red ruby. So, in a sense, rubies could be said to be red sapphires.

Thanks, Minnesota.