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