SDSS example of a "blue" galaxy (in this case, g-r = 0.63) and its spectrum. Note the prominent Ha+[NII] and [SII] lines in the red, indicating current star formation.
SDSS example of a "red" galaxy (g-r = 0.88) and its spectrum. Note that the SDSS fibre aperture is only 3 arcsec in diameter, so these are really "nuclear" spectra.