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