formation histories. Galaxies with stellar populations that formed at different epochs will have an intrinsic scatter in their colors, and this scatter will decrease as these red sequence galaxies evolve.

In simple models, the scatter in the observed color of red sequence galaxies increases with redshift as the fractional age differences between the galaxies becomes larger [@Bower92; @Ellis97; @vanDokkum98]. In more complex models that include morphological transformations, the scatter can be constant or even decrease with redshift [@vanDokkum01; @Romeo08]. Directly probing the scatter in color (as well as the scatter in age) as a function of redshift will constrain these models.

The intrinsic scatter in the $U$-$V$ colors of local early-type galaxies in the Coma Cluster is $\sim$0.03 mag [@Bower92]. Most of the work at higher redshifts has been done only in clusters, finding a roughly constant internal $U$-$V$ scatter of $\sim\!0.08\pm0.03$ mag at $0.05<z<0.8$, increasing to $\sim\!0.15$ at $z$=1.6 [@vanDokkum00; @Holden04; @McIntosh05a; @Lidman08; @Mei09; @Ruhland09; @Hilton09; @Papovich10]. To date, there are no measurements of the intrinsic scatter in the CMR for field galaxies at $z\!\gtrsim$1, because this requires accurate rest-frame colors and methods of separating star-forming and quiescent galaxies.

At high redshift, the color-mass relation is “diluted” by dusty 