Saulteaux and Anishinaabe artist Robert Houle was leading a group of journalists around “Red Is Beautiful,” the new retrospective at the Art Gallery of Ontario devoted to his half-century-long career, when he stopped in front of his 1998-99 work “Sandy Bay.” Houle, an uneasy public speaker, took a moment to steady himself before addressing the abstract and figurative piece, which bares his reflections of the residential school where he spent weekdays throughout his childhood. In viewing “Sandy Bay” in light of the recent discovery of thousands of unmarked graves near residential schools, Houle explained, he now sees in its assemblage of photographs and large canvases a divergent path his life…