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