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