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