Which of the sentences below is correct if I want to strongly emphasize that the pencil is not is not white?
- This is a black instead of a white pencil.
- This is a black, instead of a white, pencil.
- This is a black—instead of a white—pencil.
"This pencil is black, not white."
"Not white, but black this pencil is" (in Yoda-speak).
I prefer my first version, by the way.
I would rearrange it:
This pencil is black instead of white.
But if you want to keep your original arrangement, the choice with the comma is most accurate:
This is a black, instead of white, pencil.
Use the sentence with the dashes. They add the emphasis you want by setting off "instead of white" visually.