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