Muslims and Christians don't worship the same god. At least through a Google search I just did. The Christian god is the trinity: the father, the son and the Holy Ghost. Muslims deny Jesus was the son of god. So, they are denying the son part of the Christian god. So, they don't believe in the same god. As to the umbrella. I mostly see black umbrellas in my world. Was there a meeting saying most umbrellas should be black?