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