 <p>AFAIK, there is no direct answer because multiple wavelengths can combine to give the same color right? So you have the wavelengths that map to pure colors and then their combinations can give many other and the same colors. And there are several combinations that can give the same color. This is because of inteference. So you essentially are asking for a one to many mapping. </p> <p>To answer your question: There is no fixed formula. The reverse formulas will give you a range. That is the best it can get. </p>