Alkanet will give you purple, depending on how much you use.
Is this soap for personal use?
When I first started soaping and didn't have many colourants, I broke up some old eyeshadows (they come in soooo many colours), and I figured that they are only mica and probably titanium dioxide and someother skin safe (obviously) ingredients. So I ground them up into a powder and mixed with some reserved oil and added that to the soap.
I wouldn't tell you to do that if they soap was for sale, but if it's just for your use. It's a bit messy, and proper colourants are much easier, but I know what it's like when you've got an idea in your head and you want to try it NOW!!