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)(15,16)(17,19)(18,21)(20,25)(22,26)(23,28)(24,27) involution — undirected(5,6)(7,10)(8,9)(11,12)(14,19)(15,22)(16,23)(18,24)(20,28)(25,26) involution — undirected(2,4)(13,15,18,22,17,20,24,28)(14,16,21,26,19,25,27,23)(5,7,8,11)(6,10,9,12)(14,19)(15,20)(21,27)(22,28)(6,9)(10,12)(13,16,24,23,17,25,18,26)(14,20,27,22,19,15,21,28)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.