However, he was color blind, so he had to rely on the eyes of his assistant, who could easily (3)________all the seven colors: red, orange, yellow, green, blue, indigo and violet. His assistant couldalso clearly tell the difference between indigo and violet. There are two types of rainbows. Primary rainbows are the most common and have the most distinctive colors, with red appearing on the outside of the arc and violet on the inside.