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