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