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