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