The outer petals are almost white, so I have described their form using MG phthalo and MG quin red. The base of the petals have a hint of yellow for which I used DS hansa yellow medium. Here are the first washes which I worked on wet in wet. If you drop in a pale greyed down blue or voilet mixed from the three primaries into a moist petal, you will see the petal turning concave or convex. But take care to leave the highlights white. For this the amount of moisture should be just right, not so wet that the color floods the area nor so dry that the color doesn’t flow.
I worked each small part separately so the values have to be put in taking into consideration the value range of the whole flower. Else it will look like an abstract piece composed of small parts and not come together as a rose. The values are quite close to each other reaching only upto a 3 at the very centre.
Strengthened some values in the second washes.
I used DS new gamboge to strengthen the inner areas of each petal and S raw sienna for shadowy areas. A tiny bit of MG nickel azo yellow too. This color is a vivid yellow in tints and moves towards brown in heavy washes.
More areas done in the same way. The dark centre is a mix of new gamboge, quin red and raw sienna. The shadowy centres have a bit of blue.