Minecraft wiki entry for Cloud, associated text: Fast: Clouds are two-dimensional and opaque. They do not change between day and night. Their color comes frop the top of the fancy clouds. Their smallest horizontal dimensions are 8×8 blocks wide. Fast clouds in Bedrock Edition are also opaque, but remain three-dimensional. Their appearance is similar to cirrus clouds.
Fancy: Clouds are translucent, three-dimensional prisms, approximately four blocks tall and 12x12 blocks wide. At night they turn a shade of blue and become more transparent. They are similar in appearance to stratocumulus clouds.
Fabulous! graphics also affect clouds, being the same as Fancy, but also being visible through transparent blocks and water.