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