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