//------------------------------//
// The Answer 5 
// Story: Life is A Test 2: Test Harder (Quite A Bit Harder) 
// by Brony_of_Brody 
//------------------------------//

Big Blue is colour blind, and he's wearing a black hat.

To understand the logic, first consider what the chain of events would be if nopony was colour blind. If Azure Sky could see two white hats, she would immediately know that all the whites were taken and that she therefore must be wearing a black hat. If she says no, it means she's either seeing all blacks, or one white and one black.

The next pony down the line, Big Blue, knows this. If he sees that Cirrus Spin is wearing a white hat, he'd know that Azure must be seeing one white and one black, and so therefore he must be wearing black. His lack of a yes answer can only imply that Azure is seeing two blacks and eliminates the possibility of Cirrus wearing white.

Finally, Cirrus Spin realises that because neither know the colour of their own hat, he (and both of the other ponies) conclude Cirrus is wearing black.

Now let's add the colour blind pony, and see where that takes us.

Cirrus cannot be the colour blind one, because using the logic train described above, he would be able to deduce his hat's colour through logic alone, and whether he was colour blind or not wouldn't even matter.

Similarly, Azure cannot be the color blind one either. Since all the ponies involved know who the colour blind pony is, both Big Blue and Cirrus Spin would know Azure saying she doesn't know the colour of her hat would yield no useful information; no duh, she's COLOUR BLIND. Therefore, the train of logic to work out the hat's colour would start with Big Blue, and using the logic train above, Azure would realise she was wearing a black hat: she wouldn't have said that she didn't know her hat's colour a second time.

Therefore, the colour blind one must be Big Blue, and he must be wearing a black hat.