Phone makers have long given device colors unnecessarily esoteric names, but Google is going for raw descriptiveness with the Pixel phones. You have Quite Black, Very Silver, and Really Blue. The blue offering is certainly bold, and probably the most divisive choice. However, you don't even have the option of getting a Really Blue Pixel unless you're in the US. That will change, though.
The Really Blue Pixel has a white front panel and very, really, quite blue back panel. It has been reported that this limited edition color would only be for sale in the US. While it's true that you can't get it elsewhere right now, that's only a temporary restriction. The Really Blue Pixel and Pixel XL will be coming to other regions later. This news comes straight from a Google rep at the event.
As for the timing, there was no firm answer on that. We're not even sure how "limited" this limited edition will be (it's already showing as out of stock in the US). If you think the blue phone is up your alley, you should grab it as soon as it's available. You probably won't be able to get it later.