Aperture cannot mask, so you would need to round trip to Photoshop of other image editing tool. However once your flower has a color, you can use Aperture to change that color via the Color controls.
who are you steve weller? you are the only person that responded to my question. i am so embarrassed that such a company like apple did not include masking in aperture. i am presently being attacked by the family for changing over to apple while they stayed with pc and have the benefits that i cannot get with apple computers. do you work for apple?