First off, kudos for actually releasing something new in an interesting way.

That being said, they should have released all the colors at once and turned down the spawn rate. It would have been fun to hunt down the different colors, but also no real rush since they'll be back in the spawn pool every other month or so.

I think they also consider that it would be too beneficial for the hardcore user and too tiring for the casual if that was the case. They also seem to not want to run out of content yet. It sucks that it is mostly a profit driven as casual users are happy they can easily collect and hardcore users have to wait for the next content update.