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