The Colorado legislature banned people from showing their filled-in ballots — including the mail-in ballots used by most Coloradans — to anyone. On Friday, a federal judge (in Hill v. Williams) held that this violated the First Amendment, including when applied to posting pictures of one’s ballot; the court concluded that the government interests in preventing vote buying and voter intimidation can’t justify such a broad ban, which isn’t limited to showing ballots in order to further such a bribery or intimidation scheme.
The court stressed, though, that its decision doesn’t authorize people to take selfies in physical polling places, and indeed there the First Amendment rules are more government-friendly. That may well be a sensible distinction to draw: Because such places are likely to be treated as government property (whether permanent or temporary), restrictions on First Amendment activity are allowed there so long as they are viewpoint-neutral and reasonable.
For more on this general issue, see this post.