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