  We quantify the intrinsic width of the red giant branches of three massive
globular clusters in M31 in a search for metallicity spreads within these
objects. We present HST/ACS observations of three massive clusters in M31, G78,
G213, and G280. A thorough description of the photometry extraction and
calibration is presented. After derivation of the color-magnitude diagrams, we
quantify the intrinsic width of the red giant branch of each cluster. This
width translates into a metallicity dispersion that indicates a complex star
formation history for this type of system. For G78, sigma_[Fe/H]}=0.86 \pm
0.37; for G213, 0.89 \pm 0.20; and for G280, 1.03 \pm 0.26. We find that the
metallicity dispersion of the clusters does not scale with mean metallicity. We
also find no trend with the cluster mass. We discuss some possible formation
scenarios that would explain our results.
