The outcomes and their probabilities are:
YY (7/12)(6/11) = 42/132
YR (7/12)(3/11) = 21/132
YB (7/12)(2/11) = 14/132
RY (3/12)(7/11) = 21/132
RR = 6/132
RB = 6/132
BY = 14/132
BR = 6/132
BB = 2/132
-----------
Total = 132/132
Adding the two entries RB and BR: (6+6)/132 = 12/132 =