sweet tooth turning purple?

im growing a 3 plant scrog two of them are sweettooth from seed and the otheris a whitewidow clone.
the sweettooths are being flushed but last week when i stopped giving them nutes i noticed parts of the leaves and buds were turning purple.not the reddish purple you see from a nute deficiency. its turning purple!! the other sweettooth isnt turning purple and during the veg it seemed to lean more towards the sativa growth
my question
has anyone else experienced this in a sweettooth from seed? or am i growing some unknown strain?

its been noted that the sweetooth with turn purple at the end of her cycle.