Green and hard papayas can be left to ripen. Green papayas are unripe papayas with hard flesh and a greenish color. Left in a warm, airy environment, green papayas will ripen. The breakdown of pectin will cause the flesh to soften and the papaya will gradually turn yellow in color. After three to five days, the papaya will become soft and yellow in color and can be cut and eaten. If left too long, the papaya may over-ripen and the flesh may become too soft or rot, so observe and eat it promptly. The time and conditions may vary depending on the variety of papaya and the ambient temperature.