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