Blue

Feel free to disagree with this, bu I read somewhere (probably the Smash Wiki) that apparently, Tabuu is supposed to represent growing up. Examples to support this are Master and Crazy Hands being the hands of the child or creator/destroyer of the Smash universe, the fighters/characters being trophies or toys, and Smash being inside the imagination of said child.

Tabuu destroys the Smash universe, akin to how growing up causes one to lose childish urges and imagination, and renders the fighters useless as trophies, akin to putting away your toys.

This is just a rough analysis and take on it, so like I said fee free to debate or disagree.