Using the Main galaxy sample of the SDSS Data Release 5, we have investigated the correlations among color, morphology, and luminosity. We find that only within certain luminosity region the proportion of early-type galaxies significantly increases with increasing luminosity. The CM relations of galaxies also do not present single tendency, for different CM relations or in different luminosity regions, the tendencies of changes of the mean colors with luminosity are different. The mean colors of galaxies significantly increase with increasing luminosity only within certain luminosity region for some CM relations. Within certain color region the proportion of early-type galaxies also increases with increasing colors-especially for g--r color. For very blue galaxies, the proportion of early-type is weak functions of colors except u--g color. For the reddest galaxies the early-type proportion decreases with increasing colors.

PACS numbers: 98.62.Ve