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