Here´s where I am on my new painting of cheerful, sunny poppy flowers (which I found here at Weil am Rhein), a cute little tulip solar garden-light (a find at the Europa park) and a beautiful sulphur butterfly(from pdphoto.org). I wanted a true yellow here, not as warm as new gamboge and not as cool as hansa yellow medium, but somewhere in between like WN winsor yellow, but this is not completely transparent (you can see in the chart below, that it somewhat decks the black line, (colors are not reproduced exactly the same on screen)). So, for the first washes I have used a mix of the hansa yellow medium plus a little bit of new gamboge.
Wash over the petal with water and wait for half a minute or so to let the water sink in, then layer with a light mix of these two yellows (photo 1). Let it dry thoroughly and repeat this step leaving areas for the highlights (photo 2). Repeat again with a layer of Schminke translucent orange (photo 3), leaving the edges a little paler. Lift out highlights with a stiff brush. Repeat with another layer of translucent orange (photo 4). Add the shadows in the next layer. Adding just blue to the orange, will give a olive tinge to the shadow color, so add some Schminke red madder dark as well to brighten it. The layer in photo 5 has this mix of S translucent orange, S red madder dark and (very little) MG phthalo blue. Add an extra bit of phthalo blue in the stronger shadow on the inside of the petal. Paint in creases on the top side of the petal. Lift off highlights.
On a 11 step value scale, you need to get to a value of 8 to 9 in the deeper shadows, 4 to 5 in the sunlit areas and 2 or 3 in the highlights.
For the butterfly, paint wet-in-wet a mix of the two yellows, favoring the cooler yellow (photo 3). Repeat this step for the next layer (photo 4). Repeat again, this time adding the translucent orange in some areas (photo 5).