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