Executando Desafio Extra Credit:
Change the background color conditionally

Add "if" statements to check the value of the answer in the onClick()
method. You can compare it to the values stored in the mAnswers array of
the CrystalBall object using the String.equals() method.

For example, answer.equals(crystalBall.mItems[0]) checks whether the
answer equals the first item in the array or not. Change the background
color for certain answers or certain types of answers, like make it red
for negative answers and green for positive answers.