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