You could post pictures of the blanks here, and get opinions.
I have black walnut (heart wood) that runs from tan/pinkish to dark red, brown and black. European walnut tends to have tighter pores, but it depends upon where it was grown. I have some English that was grown in central Pennsylvania that is light in color, soft, and has wide pores.
Its kinda like asking what kind of maple when looking at curly maple, but think it easier to differentiate walnut than maple by looking at a blank.