In a large saucepan, combine sugar, water and lime juice; add food coloring if desired. Bring to a rolling boil over high heat, stirring constantly. Stir in pectin, mint and lime zest. Continue to boil 1 minute, stirring constantly.
Remove from heat; skim off foam. Ladle hot mixture into five hot half-pint jars, leaving 1/4-in. headspace. Wipe rims. Center lids on jars; screw on bands until fingertip tight.
Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 10 minutes. Remove jars and cool.
The processing time listed is for altitudes of 1,000 feet or less. Add 1 minute to the processing time for each 1,000 feet of additional altitude.