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