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