this is a bug in 1.7.2 through till at least 14w28b, but the version drop down did not seem to think 1.7.2 was a valid version.

*This might be a duplicate of MC-52391 but looking at his screenshots its different.*

Clouds appear to render fully, as opposed to dimmed or not there at all if above cloud level and looking through a portal. Dont have screen shots, but it wasn't looking the same through water or ice.