  Lensing tomography with multi-color imaging surveys can probe dark energy and
the cosmological power spectrum. However accurate photometric redshifts for
tomography out to high redshift require imaging in five or more bands, which is
expensive to carry out over thousands of square degrees. Since lensing makes
coarse, statistical use of redshift information, we explore the prospects for
tomography using limited color information from two or three band imaging. With
an appropriate calibration sample, we find that it is feasible to create up to
four redshift bins using imaging data in just the g, r and i bands. We
construct such redshift sub-samples from mock catalogs by clustering galaxies
in color space and discarding regions with poorly-defined redshift
distributions. The loss of galaxy number density decreases the accuracy of
lensing measurements, but even losing half or more of the galaxies is not a
severe loss for large area surveys. We estimate the errors on lensing power
spectra and dark energy parameters with color tomography and discuss trade-offs
in survey area and filter choice. We discuss the systematic errors that may
change our conclusions, especially the information needed to tackle intrinsic
alignments.
