I was been in a server that had a map with an fantastic red sky, more brilliant of the nether_world sky. How to create a world with a customized sky? I need Terrain Control or something like that? Thanks up EDIT by Moderator: merged posts, please use the edit button instead of double posting.
Maybe I misunderstand completely, but sky color is something client-side, at least I think it is. Are you sure you didn't use a texture pack or mod when visiting that server?
But even with something like Terrain Control, certain changes require also a client mod, and last time I checked, that includes changing the sky.