Three-color photoelectric data are listed for 25 galaxies in the Coma cluster and six faint dwarf ellipticals in the Virgo cluster. The correlation between standard isophotal apparent magnitude of the galaxies and their U - B values has a correlation coefficient of r = 0.94, and extends over 8.5 magnitudes. The rms deviation of the U - B correlation gives (AV2s) = 0.72 mag, excluding the two largest residuals. K-corrections are computed and listed for U - B and Q indices for z < 0.03. Applying the corrections to the Coma cluster permits the color-magnitude effect in Coma and Virgo to be compared, so as to test the zero-point difference between the clusters. The least-squares magnitude shift between Coma and Virgo is AV26 = 3.66 + 0.14 mag from the color-magnitude effect, with AV26 = 3.84 (+0.42, -0.36) required by the ratio of the redshifts, if there is no local shear to the velocity field at Virgo. The present data are inconsistent with the AbelI and Eastmond hypothesis of fitting humps in the luminosity function that requires AV = 4.7 mag. The need for a second parameter in the M = f(U - B) relation is uncertain. The color-magnitude relation is expected to be useful in estimating relative distances to field E and SO galaxies on the scale of the distance to the Coma cluster.
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Allan Sandage (1972) studied this question.