Conceived as a vibrant celebration of Mexican culture, writer-director Lee Unkrich’s “Coco” is the 19th feature from Pixar Animation Studios and the first to seriously deal with the deficit of nonwhite characters in its films — so far limited to super-sidekick Frozone in “The Incredibles,” tagalong Russell in “Up” and Mindy Kaling’s green-skinned Disgust in “Inside Out.” It’s a point worth making from the outset, not so much for political reasons (although they matter) but to indicate how this effective yet hardly exceptional addition to the Pixar oeuvre finds at least one significant front on which to innovate, even while coloring comfortably within the lines on practically everything else.

Like Remy, the rodent hero of “Ratatouille” who dreamed of working in a French restaurant, 12-year-old Miguel Rivera (voiced by Anthony Gonzalez) has just one passion in life: He wants to play the guitar. Unfortunately for him, Miguel belongs to a family of humble shoemakers where music...