Spectral and XYZ Color Functions

This is the beginning of a set of functions for working with color as wavelengths (spectral color) and in the xyY and XYZ color spaces. Current functionality includes: spectrumLabel - Add a color bar containing the visible Spectrum to a plot`s X axis. spectrumRGB - Converts wavelengths of light to equivalent RGB values (in the sRGB space). colorMatchFcn - Raw data of popular Color Matching functions (Spectra to XYZ) for various standard observers: * CIE 1931 2-degree * CIE 1964 10-degree * CIE 1931 2-degree modified by Judd (1951) * CIE 1931 2-degree modified by Judd (1951) and Vos (1978) * Stiles and Burch 2-degree (1955) * Stiles and Burch 10-degree (1959) illuminant - Raw data for the A, D65, and E standard illuminants.