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