Primal Dialga (Japanese: やみのディアルガ Dark Dialga) is a Pokémon that appears in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky.

Primal Dialga has the body shape of a normal Dialga but the color scheme is different. The blue color in its body is changed to dark navy blue, the "streamers" are recolored to orange and the diamond in the chest is altered from blue to a cherry shade red which is a sign of its berserk and savage state.

http://bulbapedia.bulbagarden.net/wiki/Primal_Dialga