After taking care in pressing your flowers, you want to preserve them and retain their natural color for as long as possible. Moisture and light are the enemies of your pressed flowers' longevity, but pressed flowers stored correctly can last several years and keep their natural color. The preservation process isn't complicated.
Place your properly pressed flowers and leaves in a single layer on a clean sheet of copier paper or newsprint. Fill the paper, but do not have any flowers overlapping. Your pressed flowers are fragile, so be careful when you lay them out.
Place the full sheet of pressed flowers and leaves into a clean file folder and close the folder. Label the folder with the type of pressed flowers in it and the date, writing with a pencil. You may wish to carefully secure the folder with paper clips along the edges.
Slip the file folder into a foil dry-lock bag. Before you seal the foil dry-lock bag, slip into it a silica gel packet to help keep moisture from possibly developing inside the bag, which would degrade your pressed flowers. Foil dry-lock bags are good to use in storing pressed flowers and leaves because they block light from your pressed flowers, keeping them bright and colorful.
Store the foil dry-lock bags in a plastic box with a lid, and add a couple of tbsp. of silica gel. Again, the silica gel, plus the lidded box, will keep moisture away from your pressed flowers.
Place the plastic lidded box full of stored pressed flowers in a dark, cool area. Heat will not fade your pressed flowers, but will deteriorate them more quickly.