Mercury is actually grayish-brown in color. It's a rocky planet, and its surface is covered in craters and plains. The gray color comes from the rock and dust on its surface, while the brownish tint can be attributed to traces of iron oxide (rust).

You might see pictures of Mercury that show a more reddish hue. This is because of the way the planet reflects sunlight, and the colors can appear different depending on the angle and lighting conditions.