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