words, all galaxies have the same $U$-$V$ color).  Each mock galaxy is assigned a value for the scatter in $U$-$V$ that comes from our simulations as described above, and we then perturb the colors by an amount that is drawn from a Gaussian distribution with width equal to the color uncertainty.  The scatter of colors in the resulting sample is then taken to be the contribution of photometric errors to the overall observed scatter.   Finally, in order to reduce random uncertainties, we repeat this procedure 100 times. The contribution to the observed $U$-$V$ scatter from photometric error increases with $z$, as one might expect, from 0.007$\pm$0.005 mag at $0.2<z<0.9$ up to 0.05$\pm$0.02 mag at $1.8<z<2.2$, but it is significantly less than the observed color scatter at all redshifts. We note that the uncertainties in the $U$-$V$ colors are smaller than the observed flux error bars that sample the rest-frame $U$ and $V$ regions. The rest-frame $U$ and $V$ fluxes are typically calculated from 2-3 medium band filters, which reduces the uncertainties.

The errors in the photometry are very small at low redshift; therefore any perturbation of the fluxes does not significantly change the photometric redshift and the $U$-$V$ color. There 