Yes the order is always the same.

A light's colour is determined by its wavelength. "White" light, like sunlight, is a combination of all the different colours.

Rainbows happen when the suspended drops of water in the air act like prisms and refract the light. When light goes through a prism, it gets bent by an amount that depends on its wavelength. The longer the wavelength the less it is bent, the shorter the wavelength the more it is bent. That means the light gets "fanned out" according to colour. Red has the longest wavelength and gets bent the least, orange gets bent a little more, etc etc.