Fill a plastic Ziploc bag with salt. Add 8-12 drops of green food coloring and close the bag. Gently squeeze and mix the salt until the color covers all the salt. Add more food coloring if the salt needs to be darker green. Pour the salt into a shallow bowl to dry.
Rub the rim of a glass with a lime slice. Dip the glass into the salt.
Shake the tequila, lime juice, Triple Sec, and Midori together with ice.
Fill a glass with ice, then carefully pour the margarita into the glass.