Literally, RED100 translates to http://xn--rs8h.com/ in my Safari browser, and so I thought, “Hey, let’s give it a go and see if my phone is smart enough to transcribe it into the right URL if I can purchase it.
The long story is, you can’t. And that’s pretty sad.
My first attempt was through GoDaddy, who simply said that it wasn’t possible. My next attempt was through 1and1.com, and they gave a more specific answer: “Domains can’t be registered with a hyphen in the third or fourth character.”