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