Pokémon Gold and Silver Versions were developed by Game Freak and published by Nintendo in 1999 in Japan and 2000 everywhere else. They are ‘second generation’ Pokémon games and were released simultaneously as twin titles, as has become the norm with Pokémon games.
These were the first proper, full-colour Pokémon games, with graphics that have been created to take advantage of the Game Boy Color‘s extended palette (Pokémon Yellow, which preceded this game, didn’t really do that; the graphics were simply colourised from the black and white originals). And you can tell from the very beginning that the visuals in Gold/Silver are a step-up from what we saw previously.