The use of tunable-color illuminants to enhance the color gamut of display devices was proposed and investigated. In particular, flexible sub-wavelength dielectric gratings (SDGs) were investigated as a possible means of realizing filters with a tunable transmission spectrum. Modeling with rigorous coupled-wave analysis (RCWA) showed a wide range of color tunability. However, tunability between the intense colors ideal for forming large color gamuts was limited. The effects of illuminant tuning on color density was also investigated.