Preheat oven to 350°F and grease a 9×12-inch baking pan with butter or non-stick spray.
Mix cake batter: In a large bowl, combine cake mix, eggs, oil, peach nectar, and food coloring (if using). Blend with a mixer until smooth. Fold in chopped peaches gently with a spatula to avoid bruising the fruit.
Bake: Spread batter into the prepared pan. Bake until a toothpick inserted into the center comes out with moist crumbs but no wet batter, 26–28 minutes. Let cool completely in the pan on a wire rack.
Prepare the glaze: In a saucepan, combine butter, cream, and brown sugar. Bring to a gentle boil over medium heat, whisking constantly to prevent burning. Remove from heat, stir in vanilla, then gradually add confectioner’s sugar until smooth.
Drizzle and serve: Once cake is cooled, spread the glaze over the top. Let the glaze set slightly before slicing and serving.