Which console family was Pokémon Gold and Silver originally designed for?

Pokémon Gold and Silver were originally designed for the Game Boy Color.

The games were developed by Game Freak and released in Japan in 1999 as the second generation of the main Pokémon series. Their color presentation and technical features were designed for Nintendo’s color-capable handheld, although the games retained compatibility with the original monochrome Game Boy hardware.

Gold and Silver expanded the series with the Johto region, a day-and-night cycle, breeding, held items, Pokémon eggs, and 100 new Pokémon species. They also connected to the earlier games, allowing players to trade and battle across generations with compatible hardware and accessories.

The Game Boy Color identity is important because the games are often casually described simply as Game Boy titles. That description is not entirely wrong for compatibility purposes, but Game Boy Color is the specific platform associated with their original release and presentation.