Are you asking because that one very different from the others? It may actually be male, it has sickle tail feathers, and a very red face. Is it different in behavior from the others?
I do not have any silkies so I can really help you with gender. However, it i common for people to think the egg is fertile, but it really a dud. The egg you posted looks fertile, but could also just be due to the age of the egg.