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