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