  We present initial results from the Dark Energy Spectroscopic Instrument
(DESI) Complete Calibration of the Color-Redshift Relation (DC3R2) secondary
target survey. Our analysis uses 230k galaxies that overlap with KiDS-VIKING
$ugriZYJHK_s$ photometry to calibrate the color-redshift relation and to inform
photometric redshift (photo-z) inference methods of future weak lensing
surveys. Together with Emission Line Galaxies (ELGs), Luminous Red Galaxies
(LRGs), and the Bright Galaxy Survey (BGS) that provide samples of
complementary color, the DC3R2 targets help DESI to span 56% of the color space
visible to Euclid and LSST with high confidence spectroscopic redshifts. The
effects of spectroscopic completeness and quality are explored, as well as
systematic uncertainties introduced with the use of common Self Organizing Maps
trained on different photometry than the analysis sample. We further examine
the dependence of redshift on magnitude at fixed color, important for the use
of bright galaxy spectra to calibrate redshifts in a fainter photometric galaxy
sample. We find that noise in the KiDS-VIKING photometry introduces a dominant,
apparent magnitude dependence of redshift at fixed color, which indicates a
need for carefully chosen deep drilling fields, and survey simulation to model
this effect for future weak lensing surveys.
