We have measured an extensive set of UBVRIJHK colors for M31 globular clusters ( 1 ) .
We compare the predicted simple stellar population colors of three population synthesis models to the intrinsic colors of Galactic and M31 globular clusters .
The best-fitting models fit the cluster colors very well – the weighted mean color offsets are all < 0.05 mag .
The most significant offsets between model and data are in the U and B passbands ; these are not unexpected and are likely due to problems with the spectral libraries used by the models .
The metal-rich clusters ( { [ Fe / H ] } \gtrsim - 0.8 ) are best fit by young ( 8 Gyr ) models , while the metal-poor clusters are best fit by older ( 12–16 Gyr ) models .
If this range of globular cluster ages is correct , it implies that conditions for cluster formation must have existed for a substantial fraction of the galaxies ’ lifetimes .