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