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