drudown idk about you but I've noticed that stem color can sometimes be a poor indicator of phosphorus deficiencies. I am guessing thats why you're asking about the stem color? I think it varies greatly by strain. I have a strain that always grows with red stems and loves it, but it also doesn't have any purple color changes in the bud or anything like that without being forced.

However, stem color can definitely be an indication of that under the right circumstances.