In a large bowl, combine warm milk, melted butter, eggs, buttermilk, 1/2 cup sugar, yeast, food coloring, and 1 tsp salt. Mix until fully combined.
Let the mixture rest 5-10 minutes to hydrate the flour. Add 3 1/2 cups flour and cocoa powder. Mix until a soft dough forms.
Knead on a floured surface for 5-7 minutes until smooth and elastic. Let rise in a warm, draft-free place for 1-2 hours until doubled.
Roll dough into a 12″ x 18″ rectangle. In a small bowl, mix brown sugar, cinnamon, and a knob of cold butter. Spread evenly over dough, leaving a 1″ border.
Tightly roll up the dough, slice into 12-15 rolls. Place in a greased 9″ x 13″ pan. Let rise 20-30 minutes.
Preheat oven to 350°F (175°C). Bake 20-25 minutes until golden. Cool slightly.
For frosting: Beat cream cheese and 1/4 cup butter until smooth. Gradually add powdered sugar and vanilla. Frost warm rolls and top with sprinkles if desired.