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