Mine did that when outside with the sun shining on them all of the time. I don't have many of these plants, but the leaves didn't turn red on all. The ones that did turn red/purple had red flowers. The ones that didn't were pink/yellow/orange/white.
If you scroll up to Nov 23, 2013 11:50 AM CST, you can see a pic of a pot of mine with multiple plants, wildly diff color leaves.
They aren't designed to be in full sun all of the time, that was kind of an experiment I did with mine. Some of the leaves just turned pale, which is apparently a sign of stress, a little too much sun. Your plant looks nice, Jonna, maybe a little thirsty.
