lol- fade is a deficiency... there will come a point eventually where she will stop taking nutrients from age (natural senescence) or nutrients will become unavailable by final flushing (forced senescence). (either way its caused by nutrient deficiencies)
When my Trichs are close to where I like them (some clear, mostly cloudy, mild amber) I will begin flushing, I will flush usually for about 9 days, I like to see some fade before the final chop, this tells me she's done with biological processing/manufacturing.
Early Purple can also be caused by cold temperature swings in the Rhizome. (bio-logical processes are slowed down from the cold, causing mild deficiencies).
Arguably, Others will keep them Green, bio-available nutrient right to the end, flush and chop. (no fade).