In a medium heavy saucepan, melt chocolate over low heat, stirring frequently until smooth. Using a small, clean paintbrush, coat insides of muffin cups with chocolate. Place muffin pan in the freezer for 10 minutes or just until set. Brush any thin chocolate areas with additional chocolate. Return to the freezer for 20 minutes more or until completely set.
Meanwhile, in a medium bowl, combine oranges, blood oranges, grapefruit, clementines, and pomegranate seeds. Peel silicone or paper liners off chocolate cups. Using a slotted spoon, scoop fruit mixture into chocolate cups just before serving. Top with a dollop of whipped cream. Garnish with fresh mint sprigs, if desired.