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