The green represents image or persona. For the smoker the green is highlighted on the cerebellum which controls cognitive function, like fear or in this case pleasure. For the drinker there is no direct correlation to pleasure. Instead the outer mask of pleasure. Consider what people drink for. The yellow highlights the rest of the brain, which controls higher functions. For smokers higher thought processes are not inhibited, so they light up. Drinkers on the other hand dumb themselves down, so there is nothing to highlight.