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