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