  The photometric evolution of galaxies in a hierarchically clustering universe
is investigated. The study is based on high resolution numerical simulations
which include the effects of gas dynamics, shock heating, radiative cooling and
a heuristic star formation scheme. The outcome of the simulations is convolved
with photometric models which enables us to predict the appearance of galaxies
in the broad band colors U, B, V, R, I and K. We demonstrate the effect of the
mutual interplay of the hierarchical build-up of galaxies, photometric
evolution, k-correction, and intervening absorption on the appearance of
forming disk galaxies at redshift one to three. We also discuss to what extend
the numerical resolution of current computer simulations is sufficient to make
quantitative predictions on surface density profiles and color gradients.
