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In some cases, they do just dry up and wither. It depends. Some of the leaves changing color happens when the plant isn't in such bad condition to wither or dry, it happens when there are some relatively minor problems. Here where I live it often happens ad example in early spring when the mornings are cold and then around noon, the sun gets strong. These sudden changes in temperatures make some herbaceous plants react that way. It also happens to the leaves that get covered by something and remain in the shade for too long. Stuff like that. Minor problems that the plant always overcomes.

Ohhhhh this makes so much sense now, thanks for taking the time to explain this to me😊