Infected Tattoo Only in Deep Shading

Tattoo that is 12 days old is infected. After two days, infection was noticed and got on antibiotics. After 4 days the infection spread to hand and other parts of tat. Got on second set of antibiotics. It is healing very slowly.

What is odd is why is the infection contained to areas that were deep dark shading and not the outline? Both done at the same time. The infected deep shaded areas fell out and are gone. Will have to go back to get touched up after a full heal, but why is it only the deep shading area?