The chromatic polynomial of the cube graph $Q_3$ is $$x (x-1) (x^6-11 x^5+55 x^4-159 x^3+282 x^2-290 x+133)$$ found computationally (Wolfram|Alpha). I think it's unlikely there will be an easier way to compute this other than the usual deletion-contraction methods.
See also:
* N-dimensional Hypercubes coloring