Briefly noted: I carefully positioned the gladiola stems on a light box. I photographed almost straight down, but at a slight angle, using a telephoto macro. I made a wide range of exposures so I could be sure of capturing both the transparent effect and the entire possible dynamic range of the subject.
In Photoshop, I placed the different exposures in a layer stack, and used masking to control the color saturation. Then I inverted the white background and used my patent pending cross-channel blending system to bring out the colors (only kidding about the patent!).
[Nikon D300, Zeiss 100mm f/2.8 macro lens, five exposures between one and ten seconds combined in Photoshop, each exposure at f/22 and ISO 100, tripod mounted.]