Miley’s been smoking some “purple kush”, which is purple weed. The purple comes from low temperature conditions and harvesting late in the flowering stage, when the red chloroplasts show over the dying green ones. The purple color is commonly believed to be a sign of HIGH QUALITY.
Miley’s is also referring to being high on purple drank. Purple drank is usually a mix of cough syrup and sprite. Other names for purple drank are: Sizzurp, lean & drank.
This video is processing – it'll appear automatically when it's done.