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