Until the early 20th century, the color of ruby was considered to range from the very palest pink to the deepest blood red. In fact, pink is just a low saturation of the color red. For example, if you put one drop of blood red dye in a glass and fill it with water, it will look pink. It was Western gemologists who started calling light colored rubies “pink sapphires” in the early 1900's, and the term continues to be used by many dealers and gemstone identification laboratories to this day.
Extract of "Introduction to Pink Sapphire" by Jeffery L Bergman, SSEF SGC