In three small, microwave-safe bowls, melts candy melts in 30-second increments, stirring in between. This should take 60-90 seconds. Spoon about ½ Tbs of each color into the bottom of each half-sphere mold. Using the back of a spoon, gently swirl the colors together to create a marble effect. Do not swirl more than 5 times, as the colors will start to mix and change to purple/brown. When you do swirl, be sure you reach the bottom of the mold. Spread to coat the sides of each mold. Let set in the fridge or freezer for about 10 minutes or until hardened. Reinforce the top edges of each mold by adding a little of the remaining candy melt with the back of the spoon. Let it set for a minute or until hardened. 
Gently remove from the silicone molds. In 6 of the empty halves, spoon 1 Tbs of the white hot chocolate. Top with mini baking chips and a few mini marshmallows. 
Warm a small, microwave-safe plate for 45 seconds. Place an empty half sphere onto the plate for a few seconds to let the edge melt to create a “glue.” Once the edge is slightly melted, place it onto the corresponding filled half and match the edge. Run a clean finger around the edge to remove any extra candy melt and smooth the edge. Repeat with the remaining halves until all of the bombs are assembled. 
To make hot cocoa, place a cocoa bomb into the bottom of a mug. Pour 6 oz of hot milk over it. Once the shell melts, stir with a spoon to emulsify. Serve and enjoy!