Here because length and frequency are interrelated, speed is not constant. Unlike in an electromagnetic radiation where the speed is equal to speed of light, whether it is a long
wave length or a short wave length, whether you go to gamma rays of very short wave length or radio waves of very long wave length. Speed is constant only length and, but in here it is not so. Then, what is the important thing? You see from sun I have got all these radiations coming, all of them reach my eye at the same time. So, I am seeing red, white, blue altogether and so I see white.