I have some pre-made Calla Lilies in white with the yellow stamen.  I need to make them Picasso with the purple in the center Except for the stamen, tonque)  and don't have time to make them from scratch and they are much cheaper to purchase in bulk.  I tried airbrushing but this was a disaster trying to avoid the center.  I even did the petal dust but it's too light.  I added alcohol to it and it seems darker but very streaky. 

I need some suggestions:

How do I avoid the streaks and make it more natural, how far up should I paint them?

AI am not quite sure what you mean, but I would love to help. Can you post a picture of what you are going for?

AFirst, can you wrap the stamen or whatever it's called with foil or plastic wrap? Then you could airbrush. I would go over the airbrush with petal dust, to darken it and give it the slight texture, too.

If you can't wrap it, you can use the dust with alcohol or lemon oil, and then wait for it to dry, and do a second coat.