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