What would be a reasonable explanation for this

I was sitting outside (it's dark here) and noticed a perfectly round object with red, blue, and green flashing lights flying through the air. It was fairly high up and moved about as quickly as an airplane would however I could not hear any noise from it. It was not headed to or from the airport and while the fair is in town, there is no air show scheduled. I was thinking a blimp, but it didn't seem big enough or maybe a hot air balloon but it seemed too high. I'm not generally a UFO conspiracy theorist so I wanted some other opinions...