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