So I am ashamed to admit that I still do not understand the difference in both appearance and method of creation of the gravity bullets from Richard, in the anime. When we first see them they appear to be like miniature pressure cannons, created within the palm of his hand. We see a green energy aura around his hand (my guess being the aura showing the audience the various level of power: green = Proto-Zoalord power level Aptom was seen with a green aura later as well, gold = Zoalord power level, blue = Gigantic etc). 

 

Yet later on, we see Richard fire red energy like attacks from the crystal substance on his hand, which appears to be energy beams. Yet, he calls them gravity bullets as well. So I'm just confused about this in all honesty.

  So does no one not have any theories regarding this, or was this simply an oversight?

I'm thinking the gravity bullets vary in color based on how much power he's putting in to them. Zoalords like Richard, and as cocky as he is seem to control levels of his power which might vary in color. I think how he was dealing with Murakami at Relics point when he shot him with the gravity bullets and than hacked his arm off with an energy shot from his zoacrystal....seemed  like he was using less power to peel the wings off of a fly.