Tomato seeds are covered with a gelatinous coating that needs to be removed prior to drying and saving.
I covered each container with 1/2 cup of water. After a week to ten days of replacing the water daily, stirring to help separate the waste from the seeds, and removing the occasional mold that forms on top of the water, the seeds were clean and ready to dry.
Once free of the gelatinous covering, my tomato seeds looked the same. Thankfully, I labeled each one at the start when they were at their most colorful. Placed on a sunny window ledge, the seeds were thoroughly dry after a few days.
Each variety is labeled and sealed in an envelope, then stored in a dark, cool location until next spring. This is the ultimate in recycling, using seeds from one season to the next, the way our grandparents grew their tomatoes. I believe this is the right way to sustain our gardens.