What would be a good substitute for bone marrow?

I have a science project and I have top do a cross section of a bone. I am using clay for the compact bone, sponge for the spongy bone, and a layer of paint for the periostium. I don't know what I will use for bone marrow though... My science teacher said that it was the consistency of er. I thought ballistics gel would work but it turns out that it melts. I need something soft and that can be shaped or molded into a particular shape. If it can be colored that would be great.