From What Sources Do Spirits Absorb Energy
 

A Spirit can absorb energy in order to manifest itself. Spirits try to manifest themselves for many reason, apparently as an orb is easier and takes less energy than full bodied.

I have seen spirits full bodied and they appeared so real, but other times it was if they had run out of energy and part of the body was an outline.

They can manifest themselves with any energy!

Happiness, anger, electricity, fire.

I would tend to agree with this... ^^^^

However, it may do well for us to realize that there are positive and negative energies that might become manifested as such too. ;)

I am wondering if it takes a lot more energy to manifest in colors. I have seen objects in bright colors but not a full body.