Blue is my favorite color.
Small world! I think blue one of the 3 true colors? 
It is one of three primary colors.
I've heard that you can only see blue if it's between certain wave lengths.
Yes when its between 450 and 495 nanometers.
Wow, that's a small range. It's crazy to think about all the colors you can't see with the human eye.
Blue
Blue is one of the three primary colours of pigments in painting and traditional colour theory, as well as in the RGB colour model. It lies between violet and green on the spectrum of visible light. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colours; azure contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering.
in the electromagnetic spectrum between 420 and 450 nanometers, which lies on the short-wave side of color wheel (RGB) blue, towards (spectral) violet.
However, the correspondence of this definition with colors of actual indigo dyes is disputed. Optical scientists Hardy and Perrin list indigo as between 445 and 464 nm wavelength, which occupies a spectrum segment from roughly the color wheel (RGB) blue extending to the long-wave side, towards azure.
Isaac Newton introduced indigo as one of the seven