  This note presents theoretical color-magnitude diagrams (CMDs) and
metallicity evolution for Galactic multi-population models coupled to stellar
evolution models for systems undergoing stripping and re-accretion of ambient
material, called ``open'' systems in our recent studies (Valle, Galli, and
Shore, 2005, A&A, 435, 551). We show that the observables for such systems, in
particular those related to the recovered star formation as a function of time,
are ambiguous -- systems with non-monotonic star formation rates can appear as
either bursting systems or galaxies with a hiatus in the star formation.
