Poinsettias are tropical plants that turn red according to day length, which in the tropics is close to 12 hours of light and 12 hours of dark. You can simulate this by putting your poinsettia in a dark place for 12 hours and in a light place for an equal length of time over the couse of many weeks. I'm not sure how long.
I too plant my poinsettias in flower gardens in the spring where they provide a nice dark green contrast to flowers, but they don't turn red and what red leaves remain from Christmas eventually fall off. When termperatures turn cool, I just let them die and buy new red poinsettias for the next Christmas. A friend has kept a poinsettia going for a decade or more inside. It is huge and rangey - too big to move into alternating light and dark so it is perpetually green, and I wouldn't call it attractive. it is merely a curiosity.