While sorting out my small treasures from “The Gift” I remembered a scene which I was unable to find as it was not underlined in my old copy.  Impelled to recover it  ( I had once experienced a paradise like the one described by Fyodor while driving across a lake during a stormy afternoon: a rainbow seemed to be reflected in the water together with a shimmering depth of colored raindrops which were falling on it while I crossed), I resorted to a search machine:
“Pattern of Elysian hues! Once in Ordos my father, climbing a hill after a storm, inadvertently entered the base of a rainbow – the rarest occurrence! – and found himself in colored air, in a play of light as if in paradise. He took one more step – and left paradise.”
Unfortunately there were no further references to locate it in the printed novel and a curious illustration was appended to the quote, since it offered a rainbow in which the blue was lying close to the red. [Cf. https://beingsakin.wordpress.com/2011/05/09/the-miracle-is-the-shortest-time/]  This mixture of colors led me to a description in “Despair”:
“I left the road and began to climb again, this time up a thinly turfed slope. Dreary and barren country.  The rattle of a truck came from the road, then a cart passed in the opposite direction, then a cyclist, then, a vilely painted rainbow-wise, the motor van of a firm of varnishers. In those rascal’s spectrum the green band adjoined the red.”
Only then did I learn that these lines inspired the new Vintage cover design for the novel [Cf Redesigning Nabokov: How Limitations Can Be a ...]