Many mayflies that in the dun stage are yellowish or pinkish color in the dun stage, turn mahogany color in the spinner stage. It always pays to capture one of the real flies so that you can match it for size and color. I like to carry a pair of high resolutions binoculars to scan the water and identify what trout are actually feeding on. My binoculars have been the downfall of may picky, selective trout.
Organza spinners don't have a lot of flotation, and they must be dressed carefully with floatant. Be sure to dress the whole fly lightly, except for the hook, which must penetrate the surface of the water so the fly will lay perfectly flat on the surface of the water.
Organza is a thin, sheer fabric traditionally made from silk. Many modern organzas are woven with synthetic filament fibers such as polyester or nylon. Traditionally a fabric used to make brides and harem women more attractive, Organza has found favor with fly tiers for several applications, such as the clear spent wings of mayfly spinners; the fabric is cut in narrow strips with the fibers running parallel. Then the strip is tied cross-wise of the hook. After the rest of the fly is tied, the cross fibers are easily picked out to leave only the fibers that were tied perpendicular to the hook. These clear crinkled fibers are lightweight and when treated with floatant will support the fly on the surface of calm water. The crinkles in the fibers give a sparkly effect just like real clear mayfly spinner wings. Organza fibers have become the most popular material for this application.