Cloud



Clouds are an aspect of a map that appear over the top of the map; they have no practical service and are merely aesthetically pleasing. They do however, always float towards the North, (though due to a bug, maps showed West where north should be. This was fixed in 1.9 pre-release 4 ) making it fairly simple to get your bearings. Before the 1.8 update, clouds existed between layers 108 and 112, floating through anything in those layers and obscuring the player's view should he/she be inside them.

Appearance


Clouds will appear differently on different graphics settings, and have a set pattern.

Fancy Graphics
On fancy graphics, clouds appear as about four block tall transparent prisms. In the nighttime they turn a shade of blue and become more transparent. Their smallest horizontal dimensions are 12 x 12 blocks wide.

Fast Graphics
On fast graphics, clouds appear as opaque planes. They have no daytime/nighttime rotation. Their smallest horizontal dimensions are 8 x 8 blocks wide.

Pattern
Unlike many things in Minecraft, clouds are not procedurally generated. With a texture pack, clouds' color can be changed to anything, meaning you could have pink clouds if you so desired. The file can be resized to any size, meaning it would be possible to have a different cloud pattern each day.

Future Plans
Notch said on reddit that he liked the idea of transforming clouds into blocks and making them collide with buildings terrain etc. It is unknown if it will be implemented in future game updates.

Trivia

 * If you switch between fast graphics and fancy graphics, clouds will be in a different place than they were before
 * Clouds always move to the north, and are thus, a reliable way to orient direction.