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