Intrinsic colors for dwarfs (blue symbols) and giants (red symbols) as a function of spectral type, derived from synthetic photometry of IRTF spectra. Solid lines indicate power-law fits to the intrinsic colors for dwarfs (blue) and giants (red), respectively. The upper panel shows intrinsic K_S − W₁ color, while the lower panel displays W₁ − I₁. For both color indices, significant deviations from 0 mag are observed only for late spectral types (later than approximately M0).