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