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