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