Ah... the purple coloring is just pigment - I suspect that the flowers are purple. When there is a lot of light (you are likely at the upper edge of the light that it wants) the leaves will express that pigment. Think "suntan". Black would be a problem, but purple is OK. But you still may want to move it a bit farther from the light - Phals like long duration (12 hours or so of light) but low intensity.