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)(14,19)(15,22)(16,17)(20,27)(21,26)(24,25) involution — undirected(5,6)(7,11)(8,10)(9,12)(13,14,18,21)(15,23,25,28)(16,19,17,26)(20,24,27,22)(2,4)(6,10)(7,8)(11,12)(13,15,17,22,18,25,16,24)(14,20,19,23,21,27,26,28)(5,7,9,8)(6,11,12,10)(13,16,18,17)(14,19,21,26)(15,24,25,22)(20,23,27,28)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.