One vertex per element, one color per generator, with an edge from x to x·s.
(2,3)(5,6)(7,10)(8,9)(11,12)(13,14)(15,23)(16,26)(17,20)(18,21)(19,25)(22,24)(27,28) involution — undirected(6,9)(10,12)(13,15,24,28,17,25,18,26)(14,19,22,16,20,23,21,27)(1,2,4,3)(5,7)(6,10)(8,11)(9,12)(13,14,17,20)(15,16,25,27)(18,22,24,21)(19,26,23,28)(1,3,4,2)(7,11)(10,12)(13,16,17,27)(14,15,20,25)(18,19,24,23)(21,26,22,28)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.