Red tips can also be caused by culture and weather. Cold nights in the spring time (which we've had a lot of here in the northeast) is one of the conditions. Lots of sun but wild temperature swings. I saw it on many trees this year, including Kathleen's Black, Aubique Petite, Valle Negra, Gino's Black, Vert, and Maltese Falcon. That last one surprised me. But I also noticed it on both Pine Oak and White Oak (which I hadn't seen it on before either). There are other variables besides the cultivar of the tree that can cause red tips and red tinting in the stems and leaf petioles. Oh yeah, I also saw it on Raspberry Latte, but I guess it's pretty much always there on that one, regardless of the weather and the soil culture :-)
Mike central NY state, zone 5a