Wash the limes thoroughly under running water.

Trim the blossom and stem ends of each lime and discard those parts.

Slice the limes thinly using a sharp knife or mandoline, then quarter each slice for smaller pieces.

Combine chopped limes with 8 cups of water in a large container. Stir well, cover, and let sit overnight.

Transfer the lime mixture to a large saucepan or jam pot, and bring to a boil over medium-high heat. Continue boiling uncovered for about 40 minutes.

Gradually add 6 cups of sugar to the boiling lime mixture, stirring constantly until dissolved. Taste and add up to 1 additional cup of sugar for desired sweetness.

Remove from heat, cover, and let sit for 6 hours or overnight to develop flavors.

Prepare jars or containers for storage and set up a hot water bath if canning.

Bring the lime mixture back to a boil over high heat, stirring continuously to prevent scorching.

Cook until the marmalade starts to firm up but is still syrupy, testing with a cold plate or candy thermometer (216°F to 218°F).

If desired, add the freshly squeezed lemon juice and food coloring.

Allow the marmalade to rest for about 10 minutes before stirring thoroughly and ladling into jars.

For canning, process jars in a hot water bath for 10 minutes (15 minutes if above 6,000 feet).

Cool jars for 24 hours, ensuring they seal properly before storing.