Elder!Nope
Bit unfair really as it's really just a guessing game. It's copper beech. I've seen some similar but much fainter colouring in young branch wood from a very large mature tree but this is the first sapling I've seen and by far the strongest colouring. Will be interesting to see how much, if any, remains in the final piece.
Does anyone know anything about this sort of colouring? For example, why does it happen and why does it fade so rapidly when exposed to the air? Or is it effectively in the moisture and fades as it evaporates?