This is a sundog, also known as a parhelion. Even though it produces the same colors as a rainbow, it is very different.

First, rainbows are caused by rain, drops of liquid water. Sundogs are caused by tiny prisms of ice in high clouds, so the colors appear on the clouds.

Second, rainbows are caused by reflection, so the sun must be behind you for you to see them. Sundogs are caused by refraction, so you must be facing towards the sun to see them.