  The analysis of the light curves of the optical counterparts of GRB 970228
and GRB 970508 points out remarkable similarities. The spectral distribution
obtained from the color indices shows that both the transients became bluer
during the increasing stage, and redder after the maximum. A main difference
concerns the behaviour of the optical fading which is well fitted by a single
power law in the case of GRB 970508 but not in the case of GRB 970228.
