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)(12,23)(13,25)(14,28)(15,18)(17,27)(19,33)(20,21)(22,32)(24,30)(26,38)(29,31)(34,35)(36,37)(39,40) involution — undirected(2,5)(6,7)(9,11,15,22)(10,16,18,32)(12,24,26,39)(13,20,28,31)(14,29,25,21)(17,33,34,36)(19,35,37,27)(23,30,38,40)(9,12,25,35,15,26,14,27)(10,17,28,38,18,34,13,23)(11,19,29,39,22,37,21,24)(16,30,20,36,32,40,31,33)(9,13,25,10,15,28,14,18)(11,20,29,32,22,31,21,16)(12,23,35,17,26,38,27,34)(19,36,39,40,37,33,24,30)(1,3,4,8)(2,6,5,7)(12,26)(17,34)(19,37)(23,38)(24,39)(27,35)(30,40)(33,36)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.