What causes blue lines along some lamellae of bone?

The blue color with H&E comes from the presence of chondroitin sulfate. I believe that when these lamellae were forming at the surface of the femur, bone formation was interrupted or slowed down for some reason. The osteoblasts ceased to secrete bone matrix - but continued to synthesize ground substance for a time. You may also see bluish lines at the outer perimeter of some Haversian canals. These are reversal lines, so called because these canals were excavated by cutting cones made up of a core of osteoclasts and later, osteoblasts reversed the process by redepositing bone into the resorption cavity.