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