According to Phrases.org.uk the meaning of “Purple Patch” is an overly elaborate or effusive piece of writing. Also, a period of notable success or good luck.
The Origin of 'Purple patches', which are also sometimes called 'purple passages' or 'purple prose', were originally a figurative reference to florid literary passages, added to a text for dramatic effect. They were the literary equivalent of adding a patch of purple material to an otherwise undecorated garment. Purple was chosen because, as well as being a distinctive colour, it was the colour reserved for emperors and other distinguished statesmen in imperial Rome. Most of the early references to 'purple patches' contain clear evidence of classical origins, many of them including Latin text.