[mbeex]

> Because the opposite of black box is clear box

Not a native speaker (never heard "clear box" as terminus technicus), but a mathematician: If it is "the (only) opposite", the relation ist symmetric. So the opposite of "clear box" is "black box" again. Skipping the injective part, "black box" would be still one possible opposite.

[nojito]

it's also known as open box or glass box and very rarely white box.

[mbeex]

> very rarely white box.

I would not consider the attribute "rare" to be appropriate here.

For example: I regularly deal with adversarial networks, and both black- and white-box attacks are quite common there.