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