Cabbage is really purple. As are grapes. Plums, purple carrots, raisins, and blackberries.
Thanks for the reply. I saw red cabbage at the store today but wasn't sure my daughter would eat it. I thought about plums but do you know if they are more black or purple on the inside? They werent very ripe but I thought about chancing it. Any other food out there that might work? I was thinking blue tortilla chips. They might be hard to shape though and I would rather use something healthier.