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