Reproduction steps:
1. Open project "AmbientBug"
2. Open scene "Main"
3. Enter play mode
4. Observe the game window
--- You should see white clouds and bright blue ocean (iPhone6NeededResult.PNG)
5. Build the scene for a device that uses a PowerVR 5 GPU (tested on iPhone 4, Galaxy S4 I9500)
--- You should see that on a device the clouds are dark and sometimes the water is dark too (GalaxyNexusDarkClouds.JPG, iPhone4DarkClouds.PNG)

Note:
--- The same bug seems to be present in the scene window (MacSceneWindowDarkClounds.png)