since the time of hubble, astronomers have learned that the blue color observed in some galaxies is the result of recent star formation. the blue regions can be seen in the following figure, where the color differences are schematically depicted. this interpretation has been confirmed by multiwavelength observations that have revealed the presence of star-forming gas clouds in galaxies hosting newly formed o-and b-type stars. sort the galaxy types according to their level of star-forming activity.