This refers to a dreamed of rain of rose-coloured petals, part of an extravagant historical fantasy Leigh Fermor indulges, imagining a rough fishermen being recognised as a lost Byzantine emperor.
‘Each carpeted step seemed to carry us into a denser rose-coloured rain of petals softly falling.’
Source: Patrick Leigh Fermor, Mani: Travels in the Southern Peloponnese, introduction by Michael Gorra, New York: New York Review of Books, 2006 (1958), p. 47