It sounds like you are interested in lycopene, as in this USDA study.
The darkest watermelons, such as Dixielee, have the scarlet gene (Scr), but apparently the USDA research used standard red watermelons, so it is not clear if the scarlet red color is related to lycopene content. Watermelon Genes
farmerdilla
jackman1944Original Author
farmerdilla
mistercross