i think the vertical lines on the yellow labs mean its not pure bred.
When I was purchasing the fish I asked owner at the lfs, about the lines, he said that it was natural for juvenile female Labidochromis caeruleus (Lion's Cove II) to show these markings. He said that they reduce in darkness as the fish age. At the moment my fish are very much still juvenile. He also said that these marking will also still show slightly in the adult fish depending on which way the light falls and reflects of the scales surface.
Check out the profile at cichlid-forum.com, in the profile pic, the fish on the bottom right still shows signs of these marking but only very slightly.
Labidochromis caeruleus (Lion's Cove II)
I have noticed in my own fish that the marking are reducing in darkness.