There have been several designs for a peace flag.
White-bordered US flag. Banner reads "Peace to All Nations".
Colombian Flag of Peace
Equatorial Guinean Flag of Peace
Ecuadorian Flag of Peace
A rainbow flag is a multicolored flag consisting of the colors of the rainbow. The designs differ, but many of the colors are based on the seven spectral colors of the visible light spectrum.
Parada Równości, Warsaw, Poland (2006)
"Pace da tutti i balconi": peace flags hanging from windows, Milan, Italy, (March 2003)
Statue of Thomas Müntzer waving a rainbow banner, Stolberg, Germany (2007)