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)(13,14)(15,23)(16,19)(17,22)(18,21)(20,26)(24,28)(25,27) involution — undirected(5,7,8,11)(6,9,10,12)(14,19)(15,24)(16,17)(20,23)(21,22)(27,28)(2,4)(13,15,16,25,18,24,17,26)(14,20,22,28,21,27,19,23)(6,10)(9,12)(14,21)(19,22)(20,27)(23,28) involution — undirectedA 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.