Need help with flower photos

[ChromeLibrarian]

I'm currently trying to document some color variations in Morning Glory flowers. I have about six different colors, from white through pinks, to a very dark purple. All the colors come out right, except the dark purple, which always turns out much lighter in color than they actually are.

I'm shooting in bright sunlight, using a 20D, and a 50mm f/1.8 II lens. I've tried using flash, not using flash, changing aperture and shutter speed, shooting shaded flowers, flowers in direct sun, and different angles of sunlight. Nothing seems to make a difference, and it's only on that one color.

Any suggestions?

[suecassidy]

I'm interested in hearing replies to your question because I recall a commerical photographer telling me once that purple was the hardest color to render accurately in a photo. This was back in the film days and i always remembered that comment. Is it different in the digital realm, I wonder? Perhaps pp is able to do that better? hmmm...

[ChromeLibrarian]

The violet shades come out fine. If you look at the top, center color below, that is the approximate shade I am having problems with. It's actually a little darker than that.

http://upload.wikimedia.org/wikipedia/commons/thumb/1/13/Color_icon_purple.png/200px-Color_icon_purple.png