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