The Maxwell-Ives criterion (MI) says that for color fidelity a camera's spectral sensitivities must be linear combinations of those for the eye[1]. W. A. Thornton's research found certain wavelengths, the “prime colors” (PC), with special importance for color vision. At CIC 6, M. H. Brill et al. spoke in favor of “cameras that have peak sensitivities at the PC wavelengths.”[2] MI and PC are not independent ideas. MI implies symmetry between the camera and the eye: the camera has its own prime colors, which should be similar to the eye's. At CIC 12, J. A. Worthey presented an orthonormal opponent set of color matching functions as a path to J. B. Cohen's Locus of Unit Monochromats (LUM), an invariant representation of color-matching facts[3]. We now present a concise method to evaluate a sensor set by comparing its LUM to the eye's. Equal LUMs would mean that MI is met, and equal PC wavelengths would tend to mean that MI is loosely met. We notice that two sets of camera sensors can have the same LUM, but differ in the net effect that sensor noise will have. A numerical noise example illustrates the point.