I don't think it is necessary. There is already the colour rarity order in the hatchery, so you can know that black is rarer than sepia. That's all that you need to know. What good would it be if there would be an added a number? The result would be same wouldn't it? If a chance would be like 10%, it still doesn't mean that after hatching 9 natties the next one will be that colour. It means you have 10% chance with the next hatch too :).