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