This is a very minor bug, but the clouds are generated in the Undergarden. It looks kinda funny, but it's still a bit odd, especially when I assume the Undergarden is underground world like the Blackreach.

Undergarden version: 0.3.8
Forge version: 35.1.13

Screenshot:

why is the sky orange?

@quek04 Actually very good question, I don't know. I think it's related to OptiFine, render distance and maybe dimension stack by Immersive Portals. Nether is under the Undergarden and the Undergarden is under the Overworld, this might affect the appereance of the sky colors? There's no clouds in the nether still and Y-axel resets everytime you dig through the dimension border.

Do you have Immersive Portals? I have a feeling it might cause that

@quek04 Yes I do. I can open an issue to them instead if the problem persists.