in order for the poinstta tohave its bracts turn red, it requires being exposed to an uninterrupted series of 'short-days'. I currently work in some greenhouses, and poinstta plants are just beginning to change bract-color, coinciding with the shorter days we are getting at this time of year in the Vancouver,BC area. thgis kind of day length (short daylight) can also be artificially simulated. Take your plant and place it, at the same time each day, in a closet or other space of uninterrupted darkness and then pull it out each day, exposing it to uninterrupted daylight. I did this to a christmas cactus and it worked. At the greenhouses we grow thousands of potmums that require short days for flowering. In the Vancouver area we have to simulate those short days by installing black plastic on all the walls and the ceiling of the greenhouse, and we have flowering mums on the market at this time of year.
Try it!