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