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)(15,24)(16,25)(17,22)(18,21)(19,23)(20,26)(27,28) involution — undirected(5,6,8,9)(7,11,12,10)(13,14,18,22,19,23,17,21)(15,20,26,24,27,16,25,28)(13,15,19,27)(14,20,23,16)(17,26,18,25)(21,24,22,28)(2,4)(5,7,8,12)(6,10,9,11)(13,16)(14,15)(17,28)(18,24)(19,20)(21,26)(22,25)(23,27)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.