This flower is not completely white, it has soft hints of violet and red-violets as well. The highlights should be kept white even if they are small areas. Even small areas will tell that it is a white flower and not a pale lilac or light colored flower. There are very few shadows in the reference photo of this flower, you can strengthen the values of a couple of them and even invent a few more to define the form of the petals a little better.
I started painting the petals and sepals here, wet in wet. The mixes are from S cobalt blue tone and S ruby red. Add a little DS hansa yellow medium to tone the violet down to get shadow mixes. Favour the red for the red-violet mix. Paint with a darker mixture on a damp wash to get the streaks. The yellow areas are yellow green made from DS hansa yellow medium and S cerulean blue tone.
The filaments have the same violet and red-violet mixes. They have a small white band somewhere aound their centres, so draw an elliptical shape passing through all of them and leave white areas. The lower portions of the filaments have red-violet bands and the upper portions, violet bands or dots.
Fill the centre area of the flower with a yellow green mix. The white bands of the filaments also have individual shadows to them, make one side darker than the other with a toned down violet mix.
The anthers are a little warmer, I added some translucent orange to the yellow-violet mix. Paint the stigmas with yellow and yellow green mixes. Add shadows with cobalt blue tone and put it some violet dots while the wash is still damp.
Add a layer of greenish- yellow and also a red violet shadow mix to the centre of the flower and add details.