Line mini-muffin tins with mini paper liners. Divide chocolate cupcake batter among muffin cups, filling each 2/3 full. Bake cupcakes until testers inserted into centers come out clean, about 10 minutes. Let cool in tins on wire racks.
Reserve 1 cup frosting in a bowl. Divide remaining frosting among several bowls. (If making 1 color, place remaining frosting in a large bowl.) Dab a rubber spatula against a tiny drop of gel-paste coloring, and mix into a bowl of frosting. Add more, drop by drop, to reach desired color. Repeat with remaining frosting. If frosting is too dark, mix in some reserved white frosting. Frost cupcakes with tinted buttercream.
To create an array of frosting shades, divide a batch of buttercream and tint each portion. We mixed different shades of gel-paste food coloring, including deep pink, dusty rose, egg yellow, lemon yellow, mauve, orange, peach, sky blue, and violet.