>Why is the temple on top of a mountain?
Because of what is below. There are deep underground structures and tunnels buried throughout time. They know they are there because they have records hidden from the masses. Same reason churches are built on hilltops.
>How many levels might exist below?
Several. There is much underground. Almost, if not all, of the major cities worldwide have underground tunnels and structures. As if an entire city was buried and built over. They know of these and use them.
>What is the significance of the colors, design and symbol above the dome?
Egyptian Blue. Used in sacrifices. Mayan Blue is similar in its use. The priest-kings were big on symbolism.
The priests infiltrated the religions and were advisors to the kings. Eventually they bred with the kings and put their own people in place. It worked then and it works now.
Infiltration not invasion.