DNA dye: Are there any natural dye for DNA (instead of artificial ones)?
Though not a naturally occurring dye, methylene blue has been used as a DNA stain. It is inexpensive and readily available. It is also comparatively nontoxic, and is used as a medication in pisciculture, so it can be found in pet stores.
If you choose to use methylene blue, save some for the blue bottle demonstration, a sensitive test for oxygen. Vitamin C or other reducing agents can be used instead of glucose.