It's been about five months since the Nexus 10 came out. In what is frustratingly becoming true Play Store fashion, accessories did not come out alongside the device. Now, however, the covers have finally landed in two colors: grey and "scarlet" (here being defined as "safety vest orange," at least as it appears in pictures).
For those unfamiliar with how this case works, on the back of the Nexus 10 there is an ovoid plastic plate that snaps in place. This normally serves no purpose, but you can remove that plate and replace it with this cover that attaches directly to the tablet and folds over to protect the screen.