Only oak leaves change right now. It'd be great if the other leaves changed color too. Maybe not spruce as that's supposed to be a pine tree (I think). And probably not jungle trees since they're tropical.

I'm not sure if we'd be able to change birch colors, but I'd like to if it's possible. Spruce colors shouldn't change though, because it's an evergreen tree. Also, jungle leaves do change. Any kind of block that uses the grass/foliage colormaps will change.

If you are going to try to change birch leaves, would you also consider the flowering oak and cherry leaves from BoP? They look out of place in winter.
Although I fear this would mean making a hardcoded exception for them and handling them differently from other leaves?