does the fake shadow only work on b/w planes?

if we specify that a mesh casts a shadow when or not when we create it, if we then put it in a group will it no longer cast a shadow? Or will that group specifically not cast a shadow, but the individual mesh will. Could then this be an alternative to the childrenShadows() function

I'm wondering why only Mesh objects can cast shadows and not the entire group or an object made using Object3d? It seems like it's not possible to make a figure using group and then giving it a shadow which is relative to each part of the figure? can you talk about that a little bit?

are there ways to personalize the shadows, colors for example? or blurriness and such, or are these all calculated and decided based on the specified light

Thank you for the reading!