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