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