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