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