The most important decision is the one to spend time together. Pick any easy recipe based the skill level of your granddaughter and on both of your interests. Chances are she will remember the time you shared and not the particular recipe you made. Nothing except the shell color which is determined by the hen breed. There is no difference in quality, nutrients, flavor or cooking characteristics.
Brown eggs are usually more expensive because the hens are bigger and consume more food.
Hard cooked eggs keep refrigerated for up to 1 week. Cloudiness indicates carbon dioxide is present. It usually escapes through the shell. A slight color may mean riboflavin is present. Blood spots are caused when a blood vessel on the yolk surface ruptures during formation.