Yes, I've noticed this with Spring Moss. I didn't actually compare the Pure Poppy straight-on and don't have the Hawaiian Shores. I think Nichole mentioned on her blog a while back that the ribbons are meant to coordinate with the cardstock and ink, not be an exact match.
That said, I think if that's the case then those ribbons that aren't going to match exactly should be one shade off so that they coordinate better. Using ribbon that's "close" but just far enough off the color of the CS and ink kind of bothers me. Then again I'm a perfectionist and look for those things.
I've slowly been matching up some of the May Arts silk ribbons to PTI colors. Kate has a great selection here:
http://www.iheartpapers.com/category...r_id=65&page=g
And it's cheap enough where one yard isn't going to break the bank if it isn't a spot-on match. Hope that helps some!