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