Will leaves always change colors when its time to ...

From my reading, it depends. Leaves change colors when they become deprived of nutrients. When you stop feeding your plants in the final weeks of harvest, they are forced to cannablize themselves. As broad vegetation leaves store sugars and nutrients (similar to how we store fat) they release them at the end of flower to keep the plant alive, to make sure the flowers don't die before they can be pollinated. So, when you begin to flush a plant, it will begin to use the stored energy (sugars in their vegetation) to fight to stay alive. That said, like you and me, no two plants are the same. Usain Bolt and I process fat much differently, even though we're both practically the same (he just trains, and I sit on my fat-arse eating chips, waiting like a well primed Inidica for a flush that will never arrive 🤪)