In resonant fluorescence line narrowing (FLN) experiments in the R1 transition of the [Cr(ox)3]3- chromophore in [Ru(bpy)3][NaAl:Cr(1%)(ox)3] and [Rh(bpy)3][NaCr(ox)3]ClO4 multiline spectra are observed at 1.8 K, (ox=oxalate, bpy=2,2'-bipyridine). For [Rh(bpy)3][NaCr(ox)3]ClO4 the number of lines and their relative intensities depend critically upon the excitation wavelength within the inhomogeneous distribution, and in time-resolved FLN experiments additionally upon the delay. This behavior is clear evidence for a resonant energy-transfer process. At 4.2 K the more common phonon-assisted process becomes dominant, manifesting itself as spectral diffusion.