  We present a new grid of stellar models and isochrones for old stellar
populations, covering a large range of [Fe/H] values, for an heavy element
mixture characterized by CNONa abundance anticorrelations as observed in
Galactic globular cluster stars. The effect of this metal abundance pattern on
the evolutionary properties of low mass stars, from the main sequence to the
horizontal branch phase is analyzed. We perform comparisons between these new
models, and our reference alpha-enhanced calculations, and discuss briefly
implications for CMDs showing multiple main sequence or subgiant branches. A
brief qualitative discussion of the effect of CN abundances on color-T_{eff}
transformations is also presented, highlighting the need to determine
theoretical color transformations for the appropriate metal mixture, if one
wants to interpret observations in the Stroemgren system, or broadband filters
blueward of the Johnson V-band.
