worrysome colouring

Hi all
Any advice on what would be turning my little oudoor late bloomer sativa dark blue purple blackish on the buds? Theres a little on th leaves too. I am getting ready to harvest so have been feeding only pure rain water for two weeks!
among thus crop i have various other strangely sativas and two nice thick indicas. All growing happily together ouwtsid my bedroom window. The smell at night is amazing!

Any advice suggesions would be great. Apologies for spelling and grammar im on my phone and no glasses!Attachment 284244Attachment 284245
Regards, south african swazi sam

Im not able to blow up your pics so i cant really see any black. As for the purple, It could be the strain or the temps could be running pretty cool at night. Either way looks like you should have some decent smoke! Good job and happy smoking!