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