We know that now, the rules were changed after others have brought it up. You can't compare Peacock with Magic, Peacock is pure colour yes but not really... lol we need a new name for these new dragons.
Peacock and Dawn Tree are pure colours but they also have hidden colours so you could call them hybrids, at least the trading portal seems to think so too giving you 2 gems for them.
So getting a Peacock from Cosmic/Cosmic is expected, a Magic and Air... no it shouldn't happen, but these new hybrids (Mythic and Cosmic) can also breed pure colours. This is new and confusing because you can't get a pure colour unless Diamond was involved... Not anymore, the new hybrids can too.
I hope that makes sense.
The new rule makes sense to me and I've never had these new colors split they act like a pure element with the only exception being the portal see's the as extra colors. I do admit its a little odd but I've done a fair amount of testing and they stay pure during breeding as far as I can tell...
My first try combo was Diamond + Cosmic, and that failed miserably for multiple times. *>.>, then I tried Cosmic + Cosmic... results ... the same! So, I moved along with Cosmic and Scorpion. I said, this should be it! I thought. Boy was I proven painfully wrong! I failed more on this combo, than the diamond and cosmic, (lol ) Then, I went back to Diamond and cosmic combo, thinking ... maybe I'll get myself a hybrid Diamond (HA!) Wrong again! After 6 tries I finally got my Saturn but no Hybrids... but that's okay. I Got My Darn tootin SATURN!
FINALLY!! So hard to get! Recommendations would definitely be Diamond and Cosmic. Soooo many fails with that combo at first, then switched to Eagle and Cosmic and another load of fails, switch back to Diamond and got it first time :-)