Shulker invisibility glitch

When I shot an arrow of Invisibility at a Shulker, It did not entirely make the mob invisible and renders the "head" white when the player is close enough.

I expected the Shulker to turn completely Invisible

The Shulker's "shell" only turned Invisible and the "head" renders white when the player is close enough.

Shoot an arrow of invisibility at a Shulker, then watch.