Bone marrow. Source
I was a little surprised to learn that this is what bone marrow looks like up close. Of course, if you were to look at marrow directly from a body, it wouldn't be this color, it'd be filled with blood and other bodily fluids. This specific sample has been bleached of all those fluids, and thus were are seeing only the color of the pure marrow.
Incase any of you didn't know, bone marrow is where our blood is made. It contains stem cells that become blood cells and keep us alive. So let's all just take a moment and give thanks to this rarely considered part of the body that is necessary for survival.