Flowering plants fading too early?

Seeing a lot of folks plants start to fade with purple, lime green & yellow leaves early in flower around wk 5. I don't see how that's possible unless the plants are under fed, cold temps or plants have natural purple genetics. I'm wondering if I'm just doing it wrong bc I fed with veg nutes until wk 3 & plants stay green well into wk 8 with bloom nutes. I don't flush just reduce nute strength, so what I'm asking is when should the fade start.

With synthetic nutrients it’s like you are always over feeding them. Plants don’t need anywhere near the npk levels your average 2 part nutrient typically provides but because you are basically force feeding every time you must ensure they get everything needed all at once.
Naturally feeding cannabis plants stop pulling down as much npk later in bloom once the buds are fully formed yet underdeveloped. This why the “fade” happens naturally around 6 week or so. They will only take from the soil what they need through cation exchange. That is as long as there are active microbes present to decompose the materials in the mix and there is symbiosis w/mycorrhizae fungi. Other wise you must provide npk in soluble form for direct absorption. This is also why you must adjust ph to the proper range when feeding nutrients; in an organic soil ph is regulated by the composition of the mix itself.
So to answer your question you should not see too much of a fade at all unless you stop feeding them nutrients altogether or your plants have an absorption (ph) issue. You are partly right they don’t always fade naturally unless you are growing with just plain water in organic soil. Perfectly normal though when it does.