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