Even if it was a semi-transparent object flying it would have a shadow, and there isn't any shadow from that object visible.
The fact that there are more areas with that colour around that place also makes me think that this is just a darker ground area.
And this is not on the middle of a desert, this is some 100 miles North of Perth.
PS: just one more thing, Google Earth has an option to show the information of the photos. This photo was taken in 2004, you can see the information
here.