They can be translucent or solid, translucent when they are dimensionally shifted, I think this is a camouflage mechanism so we can't see them. They seem able to shift up to another plane of reality something humans see as translucent, this could be their true state or home, but even though they seem translucent they are not really.
From the mountain picture the solid material spheres are hiding behind the cloud, this shows that they are intelligent, and employ stealthy techniques to hide from us the translucent sphere is not hiding behind the cloud perhaps thinking it doesn't have to. However as its sitting right over the peak, from my camera angle, I'm sure its there purposely to be seen. I have more images like these but big spheres I think should probably be in a UFO, forum. Sorry if I hijacked your thread.