The Galactic Oosterhoff Dichotomy in terms of Period-Color Relations at
  Maximum/Minimum Light
  The Galactic Oosterhoff dichotomy between Galactic globular clusters of type
I (OoI) and type II (OoII) is often characterized by a difference in the
period-amplitude (PA) relations displayed by RR Lyrae ab stars in each type of
cluster. Classical examples of OoI and OoII are M3 and M15 respectively. Here
we use multicolor data for the these two clusters to demonstrate how
period-color (PC) relations at maximum V-band light are also different in OoI
and OoII clusters.
