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