Blue may be the warmest colour, but the prurient gossip and rumour-mongering circulating the making of Abdellatif Kechiche’s Palm D’Or-winning movie has generated heat enough to obscure the truth of the film itself. But if you dismiss the salacious tabloid indignation and the leering, sensationalist headline-grabbing subject matter you’ll discover a work which is, at heart, a tender and deeply…