Could you post some regular color photos for us to take a look at? Full plant and any problem areas included...
Calcium and Magnesium deficiencies generally present as rusty or brown spots on the leaves. My research indicates purpling stems can be everything from genetics to various stressors, including of course nutrient lockout and/or PH and temperature.
My personal opinion is purple stems are a possible symptom, but not one to try and diagnose anything from. Equate it to telling your doctor you feel a little tired sometimes.
I felt exactly the same way when Shiggs pointed it out to me in my tent. I tend to over complicate things, so rather than level my lights I'll try and figure out a way to tilt my house. ;-)