[Cailean]

Dewy, I noticed that the white rose shots are a shade or two darker than the reds... I just happened to have read about this somewhere... In any of the 'auto' modes, your camera will always seek to make the image overall grey (18%, actually) by adjusting the exposure. To shoot a predominantly bright white subject, you have to over-ride the exposure... you can either go manual, or some cameras have an EV compensation feature to brighten or darken the photo.

I'll try to track down where I read that...

EDIT: Found it... http://www.shortcourses.com/using/exposure/chapter3.htm