You assume that Leaves with 8 identical contents (such as Air, or the Stone underground) wouldn’t be optimized to one single Leaf instead of split into tinier and tinier Leaves. And I am sure there will be easy ways to optimize Colors of those Leaves for Rendering too, not to mention the World doesn’t keep all the Blocks loaded, it only keeps the visible Blocks loaded, and the Blocks that Entities are actively changing or asking for.
With the Colors I should specify that they are only going to be sent to the GPU for fast rendering.