You can find the Court’s opinion here. The Court, and particularly Justice Roberts, leaves open the possibility of an as-applied challenge to the law later upon proof that voters are actually confused by the designations of the candidates’ party preferences on the ballot (thinking that this is really a party primary).
I must say that I am pleasantly shocked by this outcome from the point of view of the blanket primary, and think it will reinvigorate efforts to enact such a system in California. [Disclosure: I was on the legal team drafting a similar measure that appeared on the California ballot a few years ago.]
On the other hand, I am very troubled by the Court’s discussion of facial challenges in election law, and especially what that’s going to mean for the Indiana voter identificatiion case.