I photographed this dahlia in our flower garden under diffused light. The cloudy day allowed the light to spread evenly over the subject. Diffused light which is common on cloudy days helps to bring out full color and eliminate unwanted harsh shadows. It is especially good for photographing flowers. This composition was achieved by placing the camera below the subject on my tripod and pointing the cam at 45 degrees upward. I purposely backed off the macro to allow the green background on the RH side to include in the image.   It adds interest and color contrast.
Nikon Capture D1X, Sigma 50mm Macro at F4, 1/250 sec. Polarizer filter used to reduce glare on the yellow pedals.
Dan