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