User blog comment:ChishioKunrin/Dust: Fire! Water! Lightning! Energy?/@comment-24435688-20140822042944/@comment-4010415-20140823124857

Red is fire, so I don't think red Dust would create storm clouds. Besides, the narrator said that, when Dust is combined, it forms a new type with a new, unique effect. So, a new color of Dust won't necessarily have a combination of the effects from the Dust used to make it. This sounds a lot like a chemical reaction, which is where the two reactants change on a molecular level to form an entirely new substance. This new substance can be of a different consistency, color, state of matter, etc.

Given that combining Dust could be a process of getting them to go through a chemical reaction, we don't know for sure what colors make what. For all we know, purple Dust could be created with blue and green Dust.