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Maybe that color change is caused by lower chlorophyll concentration in younger leaves' cells, or chlorophyll a to b ratio differs between younger and older leaves. All I could find is that the chlorophyll a to b ratio in higher plants is 3:1, but there's little data if that ratio ever changes.

That color change is especially noticeable in conifers, but I've seen it in trees belonging to other divisions.

Color change

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    $\begingroup$ My guess would be that the structural metabolites and waxy cuticle that give these leaves rigidity and protect them from the elements can't be produced in these tips of new growth without stunting their development (note that the branch tip is still green and not yet woody). Conifers have some of the toughest cuticlular waxes in the plant world, and I know that a property of these waxes is that they change the apparent color characteristics of the leaves by reflecting or absorbing certain wavelengths of light (it's what makes the blue spruce blue). $\endgroup$
    – MikeyC
    Jun 3, 2021 at 21:18

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