One vertex per element, one color per generator, with an edge from x to x·s.
(1,2)(3,8)(4,6)(5,7)(9,10)(11,17)(12,15)(13,16)(14,19)(18,23)(20,22)(21,24)(25,26)(27,33)(28,32)(29,30)(31,34)(35,37)(36,38)(39,40) involution — undirected(9,11,13,19)(10,14,16,17)(12,18,20,24)(15,21,22,23)(25,27)(26,33)(28,39)(29,36)(30,38)(31,37)(32,40)(34,35)(1,3,5,4)(2,6,7,8)(9,12,13,20)(10,15,16,22)(11,18,19,24)(14,21,17,23)(25,28,31,29)(26,30,34,32)(27,35,37,33)(36,40,39,38)(10,16)(14,17)(15,22)(21,23)(25,29,31,28)(26,30,34,32)(27,36,37,39)(33,38,35,40)(1,4,5,3)(2,6,7,8)(11,19)(14,17)(18,24)(21,23)(25,30)(26,28)(29,34)(31,32)(33,35)(38,40)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.