Sony has been dropping hints about a new color on Twitter, gold! As you remember, the Xperia Z3 came in "Copper", so it wouldn't be completely weird.
It's been a while since we had an Xperia with a "Gold" color option.
We doubt Sony is thinking actual gold like the 24K gold-plated Xperia P it gave away as a contest prize in late 2012. We doubt it will be actual 24K gold, but the August 3 (next Monday) is going to reveal it to us.
