This paper reconsiders the Luther condition from a spectral and colorimetric point of view. The projection of spectral to colorimetric space is based on matrix R theory. The basis of matrix R spans a FCS (Fundamental Color Space).The spectral colorimetric design for color sensors is discussed based on FCS by clarifying its geometrical structure in relation to the orthogonal color matching function and the FCS basis.Since opponent-color model is useful for appearance-based color imaging, the paper highlights the opponent FCS with perfect orthogonality and introduces a vectorial quality factor Vq for the spectral-colorimetric evaluation of digital cameras. The spectral response to unit monochromatic stimuli is visualized as a 3-D locus that clearly shows the spectral mismatch with Luther condition. The measured Vqs are compared with Neugebauer's q-factors and also Vora & Trussell's ν-factors.