the best part of the buckeye is underground. thats the part they sell as blanks. you can produce the blue and black color by getting it to mold. i have a burl that i coated in mayo and stuck it in a black plastic bag and put in in the sun. the burl was plain yellow when i dug it up 3 weeks ago. i just checked on it and its molding already and im starting to see some black streaks. i never tried it on the trunk of the tree but it should still work. if you have enough, try a piece.