Wiktionary
purple patch
n. 1 A period of excellent performance, where nearly everything seems to go right, work properly, and contrasting with a more general lower level of performance. 2 An ornate or elaborate section of a written work, a patch of purple prose
Usage examples of "purple patch".
Randy tapped the ragged purple patch that was merged into Willa Jean's back.
You see, Key West's warm damp air had been paradoxically good for his rash: the only blemish still visible was a dark purple patch on his forehead.