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