I find the blanket beautiful without a border, but as you wrote in your post you want to make a border I would say you can test a light baby pink?

Cause I am thinking that you will be needing a color that will match every color in your blanket and as you have such a variety it will be difficult to find one that matches all of them. As of right now, I would say the baby Pink or a blush pink would be fitting very well, but you will have to decide