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