The shape changes from box to box by a fixed rule. Which answer figure (a)–(d) comes next?

Each step the shape gains one side (3, 4, 5, 6 sides) and its colour switches between orange and white. After the white hexagon comes an orange shape with 7 sides: (a). (b) has the right number of sides but the wrong colour, (c) adds two sides and (d) adds none.