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