The published J, H, and K band photometry of Frogel et al. (1983) for a sample of over 350 red giants in 33 galactic globular clusters, which covers the complete range of metallicities found in globular clusters, is used to derive a set of empirical relations which allow to predict the intrinsic colors of Population II giants as a function of metallicity and absolute visual magnitude. These relations can be used directly in programs of population synthesis which combine populations which have different metallicities. Using the relations obtained, predictions are made for the numerical values of the latter, for a subset of clusters from the sample which shows significant deviation from the mean behavior of the clusters.