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