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)(14,18)(15,21)(19,24)(22,25) involution — undirected(5,7,8,12)(6,9,10,11)(14,19)(15,22)(17,23)(18,24)(21,25)(27,28)(2,4)(13,14)(15,20)(16,18)(17,24)(19,23)(21,26)(22,27)(25,28) involution — undirected(6,10)(9,11)(14,18)(19,24)(20,26)(27,28) involution — undirected(7,12)(9,11)(13,15,16,21)(14,20,18,26)(17,25,23,22)(19,27,24,28)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.