We have performed photometry in B and V of the field of the triple system PSR B1620-26 in the globular cluster M4. Our images were taken with two two-dimensional imaging photon-counting detectors, which permitted deep exposures to be made without saturation. Photometry of the proposed optical counterpart of the second companion of PSR B1620-26 was obtained, yielding a magnitude V = 21.30 +/- 0.08 and a color B - V = 1.32 +/- 0.20. The color index has not been successfully determined previously. These values locate the counterpart on the main sequence of the cluster color-magnitude diagram and lead to a mass determination that is consistent with a 0.48 Msolar cluster main-sequence star.