Howdy Mashpee459. In my experience, the purple color is normal. I have noticed that the stems exposed to a greater amount of light, tend to darken and turn purple. The ones that I have seen, on my plants, have turned only on the side exposed to the light and not all around. Some strains even produce leaves with a similar purplish hue. I have not seen any adverse effects to the plants from the color change.
Good luck with Your grow.