I know this rose looks yellow, but it was actually snow white. You are looking at the color of light coming up through the rose bud. Phyllis helped me construct a small stage set for this photo (and the others in the series). We cut the stem close, and positioned the rose in a small, clear plastic cylinder. Next we lit the cylinder from the sides with LED lights. I covered the whole thing with black velevt cloth up to the edge of the rose blossom.
Finally, I made sure the room was entirely dark (except for the LED lighting from beneath the rose), and photographed straight down on the inside of the blossom.
Related image: Camellia Light.
[105mm f/2.8 macro lens (157.5mm in 35mm terms), extension tube, 30 seconds at f/36 and ISO 100, tripod mounted.]