The phrase "blue marble" refers to our planet Earth from space. It highlights the fact that our planet looks like a beautiful blue sphere when seen from a distance. Full definition
It is not anyone's place to judge while on this little blue marble! (religion.blogs.cnn.com)
I am wearing the blue tights today with my black dress, blue marble ball necklace that went on sale two months ago, and black boots. (reviews.anthropologie.com)