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