Cut melt and pour soap in to small cubes and place in a microwave safe bowl.Microwave in 15-second bursts, stirring in between each burst until completely melted.Mix in any colorant and fragrance.Working quickly, add in salts and stir to combine. Immediately pour into molds.If soap hardens while pouring, reheat in 10-second bursts.Allow to harden for 30 minutes or until firm before removing from mold.