A Happy Flashback is pretty much Exactly What It Says on the Tin, a Flashback to a happy time in a character's past. Frequently they have a drastically different color palette from the rest of the film/tv show in keeping with most Flashbacks. It'll be very bright, warm and colorful (possibly even supersaturated with color) or almost completely white from the brightness, or in simple sepia tones [...] [tvtropes.org]