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