The first Diablo has a very local setting. The game starts and ends in the town of Tristram, and the sixteen-level dungeon lies entirely within and beneath the cathedral on one side of town. The colors are dark and dreary. The music in the dungeon is unsettling and contributes to the oppressive atmosphere. Screams and moans echo through the halls, pathways are often twisting and narrow, and the low resolution means ranged attacks frequently come from off-screen unseen demonic beasts. No matter what, you always feel like you are going further down into the beating heart of terror. The jangly acoustic musical theme in Tristram is an audio relief every time you return from the dungeon.
The bits of color found in the game come from the impressive magic spells, and certain areas contain bright rivers of water, acid, or lava. It is certainly not a game devoid of color, and the use of light is judiciously used to enhance the overall atmosphere.
The world of Diablo 2, in contrast, practically bleeds with color. While rainy, the first Act of the game is a lush green field. Act 2 takes place in a bright yellow desert. Act 3 takes place in a darker, more frightening jungle environment, but it's not until the fourth act, in Hell itself, that Diablo 2 returns to the claustrophobic feeling of its predecessor. Obviously, the size of the world you explore in Diablo 2 is far larger; the return to Tristram is merely a quick stop along the way in a much bigger adventure.