Wrap the inside of a metal bowl, that holds about 12 cups, in plastic wrap. Get all of the sides so none of the ice cream touches the metal.
Place the bowl in the freezer for 15 minutes.
With an electric mixer, beat the lime sherbet on high until it's soft enough to spread. Add in a few drops of green food coloring if you prefer it stronger in color.
Spread an even layer of the lime sherbet in the metal bowl with a spatula, but leave a dome shape in the middle to be filled with raspberry sherbet. Place the bowl back in the freezer for 20 min.
Beat the vanilla ice cream on high until soft and then spread a thin, even layer over the lime sherbet. Place the bowl back in the freezer for at least 15 minutes.
Do the same steps with the raspberry sherbet, adding a few drops of red food coloring.
Add in the chocolate chips and beat on high until the sherbet is soft.
Fill the rest of the bowl with the raspberry or pink sherbet and place in the freezer, overnight, until it's completely hardened.
When the sherbet is frozen, remove by turning the bowl upside down on a cutting board. Take off the plastic wrap and then slice your adorable watermelon sherbet bombe cake like a normal watermelon!