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