Diamond, Pearl and Platinum Cartridges are grey. The black HGSS carts were a special edition thing exclusive to HGSS and BW/2.
They both use infrared connection.
Source: decades of playing Pokémon, owning authentic multiple copies of almost every single Pokémon game (games in question: Diamondx2, HGx2, SSx2 Pearl, Platinum x2, Black x4, White x2, W2x1, B2x1)