One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,4)(5,6)(7,9)(8,10)(11,12)(14,20)(15,21)(16,17)(18,25)(22,28)(23,24)(26,27) involution — undirected(5,7,8,11)(6,9,10,12)(13,14,17,22,18,23,26,15,19,21,27,24,25,28,16,20)(6,10)(9,12)(14,21)(15,20)(22,24)(23,28) involution — undirected(2,4)(13,15,16,23,25,22,27,14,19,20,26,28,18,24,17,21)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.