Prismatics - why purple?

[Ukase]

So...when I get one of these, I see the purple lettering. Why? I have been conditioned, in a sense, to expect those purple letters flashing across my screen to denote something "very rare". And I've done two story arcs today, and in the midst of each one, I've gotten a prismatic. 

I wasn't keeping track, but I think I get a prismatic at some point during every arc. So, shouldn't these be orange, and the monstrous aethers be yellow/uncommon? 

Just curious what the rest of you think. 

[Scarlet Shocker]

They should be Indigo but the Blue Spectrum got borked before you reached the city proper!

[biostem]

1 hour ago, Ukase said:

Just curious what the rest of you think. 

From my understanding, they *are* very rare - it's just that some content gives them as a guaranteed drop.  It's kind of like how running your first market Crash always gives you a purple recipe...