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