Required: Illustrator 9+

1. Create the flower paths

First create the paths of the flower with the Pen Tool.

2. Apply Gradient color

Select one of the petals, fill it with Radial Gradient (pick similar colors as shown) and select Multiply in Transparency pallate.
Select the un-filled petals, use the Eyedropper Tool, click on the gradient petal to copy the fill. You might need to adjust the gradient fill of each petal with the Gradient Tool.

3. Filament

Create a filament, fill it with Linear Gradient and select Multiply in Transparency pallete.
Then duplicate it.

4. Center

Use the Ellipse Tool, make a circle, fill it with Radial Gradient (as shown) and select Multiply in Transparency pallate.

Final

Duplicate the flower and lower the Opacity (Transparency).