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