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