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