use of a more shallow DOF would help in this image by smoothing out the greens in the background and putting more focus on the dahlia--right now the detail in the background fights the flower for attention.
The red flower is dominating as the subject. That said, the challenge was complementary colors. Yes, green is present but not presented as an equal enough to compliment the red. This is just what popped into my head and may not be correct. Nice photo and choice of subject.
6 - Nice. Would like to have seen green incorporated a little more 'somehow', perhaps a slight variation in the lighting for added depth too, not sure. Also seems a little unbalanced compositionally.