I went for the shape of the letter, rather than the colour-after all the quiz setter couldn't put a white letter on the white paper. If its not right, I'd be very interested to see what other answer ABers come up with.
I am also stuck on this one IF it was after eight then it could have been pictured in white with a green background as are some of the others. But it is the nearest shape There isa small green f on fresh mint tic tacs but it isn't quite the same shape . Still puzzled.