Look at the orange and the blue cells in each grid. Which grid is the odd one out?

In (a), (b), (c) and (e) the number of orange cells equals the number of blue cells (2 and 2, 3 and 3, 1 and 1, 2 and 2). Grid (d) has 3 orange cells but only 2 blue cells, so it is the odd one out.