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