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