Here is what I`ve worked on till now: I would have liked the whole flower to be a little more on the warmer side but using hansa yellow medium as the underwash has sort of restricted the color range to here. Of the options I had, Schminke auerolin modern, Winsor and Newton winsor yellow, Daniel Smith nickel titanate yellow(semi transparent) are all on the cool side. DS new gamboge lifts a bit so I didn`t use it in the under washes and S Indian yellow is warmer but also a little less vibrant (less chroma) than new gamboge. In any case, I love working with yellow!!
For yellow flowers or any other yellow object its important to get to the depth of yellow hue (through layers) that you want to reach before adding in the shadows (or other colors) as its difficult to add it later through glazing because other colors so easily overpower yellow. A bit of raw sienna and translucent orange added here on the unfinished petals towards the right hand side.
I`ll let the photos do the talking here:
I keep softening the right hand edge of the lower left half of the petal for all layers:
Stamens have a base coat of hansa yellow medium and the anthers have new gamboge.
S mauve and translucent orange gives a nice brown for the shadows on the wilted flower. Adding raw sienna to this makes the brown a little intense.