Color formation of fluorescent materials is not feasible with the usual methods used for nonfluorescent colors. Realizing the need for certain textiles that are dyed with fluorescent colorants, a technique was developed based on rising certain dual-monochromator measurements of the spectra of fluorescent colorants. To accomplish this formulation, a new spectral quantity independent of illuminant was developed for all fluorescent colorants. This is termed RELEX, which describes the relative excitation of the colorant. When this quantity is weighted by the spectral power distribution for a specific illuminant and factored for absorption by all ingredients in a mixture of colorants, the proper fluorescent emission is obtained, which can be added to the spectral reflected radiance factor, beta(s), for that mixture. Consequently, match prediction can be done for spectral radiance factor, beta(T), curves of fluorescent materials using an iterative estimation algorithm.