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