Prepare cake mix as directed on package, adding vanilla to batter. Tint cake batter orange with 1/4 teaspoon each yellow and red food color.
Bake as directed on package for cupcakes. Cool cupcakes on wire rack.
Mix desired food color into vanilla frosting (see Tinting Frosting Tip). Frost cupcakes. Place chocolate frosting into small plastic bag. Snip off a tiny corner of the bag. Squeeze out 3 thin circles of frosting onto each cupcake, beginning at the center. Starting at the smallest circle, pull frosting through all three circles using a toothpick. Repeat at even intervals 5 or 6 times around the cupcake.
For additional decorations, place purchased plastic spider on top of cupcake, if desired. (For an edible spider, use black gumdrop for spider body, and pipe 8 legs of frosting around gumdrop.)