purplish leaves on Lou Sneary Blue Bird

[orchids44]

I purchased a Lou Sneary 'Blue Bird' in early June from a very reputable orchid nursery at our orchid meeting last month, about 6 wks. ago. I have it indoors in a south window but about 6 feet from it. Our humidity level is 50-70% and have 2 oscillating fans circulating 24/7. I spray the roots and leaves daily. It's been fertilized twice with a very, very weak MSU. I've read that purple leaves can mean a magnesium deficiency.
Anyone with 'Blue Bird' or vanda experience please help. Is this normal or can I do something differently. As you can see from the picts, it's mounted on tree fern, it was bought like this. The roots seem very healthy. Thanks for any advice you can offer.