When things are peachy, they're wonderful. If you're unhappy, it's usually best to be honest about it, rather than pretending everything's peachy.
Peachy is an informal adjective that's mostly used by North Americans. You might hear a sports fan talking about how peachy things look for their favorite team, or a neighbor describing an absolutely peachy day at the beach. Every once in a while, you might even hear the term peachy-keen used this same way. It's even more common today to use peachy in a sarcastic or ironic way.