You CANNOT use liquid food coloring---that will ruin the candy. You CAN use a paste or power food coloring purchased at a craft store like Michaels, Joannes etc or a cake/candy supply store. Also some gourmet cooking stores will have the right coloring.
You can also buy candy melts from the same type of stores. They have red and pink candy melts. Also seen candy melts at Walmart in the craft/sewing section of the store.