Electric Chameleon was right. You can spray paint silk flowers.
Here is a site you might want to check out.
Coloring Silk Flowers
Cindy Piccoli gives new life to plain, dull silk flowers by simply spraying them with paint.
Use a water-based floral spray paint on any flowers made of a porous fabric. Water-based floral paints are not toxic or flammable like regular spray paints, and they don't make the silk stiff, as many other paints do. If you are buying flowers specifically to paint them, look for the low-cost white petals rather than the more expensive colored ones.
Steps:
Shake the can of paint for one minute, then spray each flower lightly. If the color is too intense, spray the wet paint with water to dilute it.
Let each flower dry for 30 minutes, or use a hair dryer for faster results.
To add a second color to the edges of the petals, spray the paint into a pan or bowl, and dip the edges of the petals into it. To soften the color, spray the flower with water.
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