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)(15,22)(16,27)(17,21)(18,20)(19,25)(23,26)(24,28) involution — undirected(1,2)(3,4)(6,10)(11,12)(13,15,17,25)(14,19,21,22)(16,26,18,24)(20,23,27,28)(2,4)(13,14)(15,19)(16,27)(17,21)(18,20)(22,25)(23,24)(26,28) involution — undirected(2,4)(5,7,9,8)(6,11,10,12)(13,14)(15,23)(16,20)(17,21)(18,27)(19,24)(22,26)(25,28)(5,8,9,7)(6,11,10,12)(13,16,17,18)(14,20,21,27)(15,24,25,26)(19,28,22,23)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.