Maybe others have already observed. But I just saw it today that the kingdom stars change from white to green to blue to purple every 5 levels. All purple is what it is at 20. After that, it could be orange and cyan. These are the colors of the increasing rarity. 
With Boss troops, there might be red stars too. 30 to 35. Will there be a boss troop from all kingdoms then? Mind is blown. 
You can already see this in-game by checking any kingdom’s Power requirements.
Nobody knows outside of the devs. That said, it is not outside the realm of possibility multiple years down the road. However, without some serious powercreep regarding obtaining Orbs of Power, obtaining 34 Boss troops (at 8 Power orbs each) is all but an impossibility.
Wow, you checked that easily enough. I didn’t even bother checking. But yeah, somehow it never occurred to me to have a look at these colors. Thought it is cool to share. And then, the boss thing struck my mind.
Nope. No red stars whatsoever.
It’s so you can use them as Christmas lights (or the holiday of your choice).
