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