I was thinking, since amber comes in October and achromatic in November... Maybe there should be a higher probability to hatch in the other colors (probably not, like, albino but still) during these months.
Or, maybe, every day/week a certain creatu egg has a higher chance of hatching in certain colors. I.E; on the first week of December, there's a higher possibility to hatch a Sirleon in the uncommon or rare colors. (The only thing that would be a problem is that it would have to be a very slight increase, otherwise people will be grabbing eggs like crazy and buying hatches.)
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I would also like more frostlight creatus this winter! Especially for the CS ones without a frostlight effect and for Tesuris. Mmm... frostlight Tesuri... *drools*