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