"Gold" and "Silver" were first publicly showcased at the 1997 Nintendo Space World Expo in Japan, becoming the most popular exhibit at the program. Unlike the previous game in the series, "Pokémon Yellow", the new titles were announced to be more than a small upgrade to "Pokémon Red" and "Blue". Instead, they would feature a new storyline, a new world, and new species of Pokémon. "Gold" and "Silver" were designed for the Game Boy Color, allowing them full color support and more detailed sprites. Other additions that were shown included Pokémon breeding, held items, an in-game gadget known as the PokéGear, a real-time internal clock, and backward compatibility with the previous games in the series.