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