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