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