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