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