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