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