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