First, let me say that I am not a professional or even a very good amature photographer, so you may want to take my comments with a grain of salt.
Meeting the Challenge / Title: As people said, the yellow stands out a bit more than the green. But I would say that it still meets the challenge. Maybe if you had incorporated something about the green leaves into the title, that would have drawn attention to the green in the photo.
Camera Work: Hmm, okay. I am going to at the same time agree and disagree with those who say that a sharper, more detailed image would have been better. I agree because with a close up like this, you want the detail to be present. However, I think that your shot as is looks like a painting. It is soft and delicate, and makes me feel relaxed and close to nature. There is enough definition to the edges of the petals and the color differentiation in the petals is clear. If that had not been the case I would have said that I very much do not like the soft focus, but as it is, I do.
Image Dimensions and Filesize: No real problems here.
I hope this helps! Feel free to PM me if you have any questions.
Edit: My sister just came in the room .. "did you take that picture?" I said no and she said "Oh. Looks good." :-)
One of the reasons I didn't enter this challenge was because I was not creative enough to think of a picture that exhibited complementary colors and didn't involve a flower... I see that you too have failed at at least one of these. The photo is a bit dark, and rather noisy. 3
love the colour, but the shot really lacks a good focus, it's quite soft...maybe that was intentional, but I would have like to have seen a really crisp shot