Very few of the dyes commonly (or uncommonly) used in cytometry have narrow
enough emission spectra to be described as fluorescing only in green
(520-530 nm for the sake of this discussion); there is almost always some
fluorescence component in the 570-580 nm region, and often detectable
fluorescence well above 600 nm. Fluorescence from inorganic materials,
e.g., uranium or the rare earth chelates, is more monochromatic, but I'm not
sure these materials would be excited significantly at 488 nm. Among the
existing organic dyes, the BODIPY series from Molecular Probes have narrower
emission spectra than most others.
-Howard