What are the coloured lines on the cover wrap preview?

From version 1.9.20 the print wrap preview in the Covers page shows guides, when "Show the guides" is ticked: the bleed that KDP trims away (tinted), the trim line and the spine folds, the text-safe lines that text should stay inside, and KDP's barcode area, labelled. They are only in the preview and are never part of the file you download. Use them to check that nothing important is near an edge before you upload the wrap to KDP.