A photo would be great. What kind of orchid is it?
Usually purple edges are the equivalent to tanning in humans. The plant segregates a pigment called anthocyanin (the equivalent to melanin in humans) to help it cope with high light levels. It is not a bad thing unless the light levels are too high, which can cause leaf burn.
Without a photo it might be just guessing but it seems you're giving the plant too much light.