I used stock photos as examples.
If you search those images and read the statements - they will explain 'I am 3 weeks from harvest date" etc.
My personal experience is not just in my grow but observing the color changes in other's grows too.
Just like trees outside - as they progress through life, the leaves return the nutrients stored in them, back to the plant. The discoloration in trees is the same as you are observing in the plant.
"Chlorophyll is the pigment located on the chloroplasts of the plants that reflects the green light. The light captured in this, becomes the food consumed by the plant, through photosynthesis." so those sun leaves are meant to decay.
You have 3 weeks to go ; ) new growth should be healthy, buds hairs nice n white, pointy, trichromes forming, etc..