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