Other causes for purple Phalaenopsis leaves besides high light?

[MT-Phal]

i've also read that a lack of phosphourous(?) can cause a purple tinge on leaves...

[AboutOrchids]

A botanist once explained to me that some plants have new growth that's not green as a way to discourage hungry critters. Their preference is tender young green growth, and they ignore the non-green growth, thinking it's old or dead. I don't know if this adaptation applies in orchids, but the logic would apply.