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