Even if there is equal probability for a ball to be white or some other color, it's not 1/3 because its not simply WN, WW, NN, it's WWWN, WWWW, WWNW, WWNN for the posibilities that still exist (out of the ones not already eliminated by the first 2 balls being white).
And the assumption that there is an equal probability for the balls to be white or not-white assumes only 2 colors of balls exist and that they exist in equal numbers... So yeah, not "too complicated" but as complicated as it needs to be as mmiguel mentions.
I honestly have to maintain it's flat out not solvable currently.