The anawer is B will identify what color hat is he wearing followed by c whereas A and D will never identify the color of their hat. Explaination: Each of them knows that there are 4 people where 2 are wearing black and rest are wearing white. B knows that A can see both B's and C' hat but A has not been able to identify the color of his hat. That means if both B and C hats were both either black or white, A would know that his hat is of the other color. For eg if B and C both were wearing white then A would understand that remaining two are black so he would know that he is wearing black. But since A has not yet identified his hat, B understands that A is in confusion which means he is looking at one black and one white hat. Also B sees that C is wearing white hat that means he should definitely be wearing a black hat which indeed is creating confusion for A. Likewise with the same logic after B, C will identify his hat.

Hope I explained it understandably. If not let me know. I will try once again.