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