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