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