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)(11,13)(12,14)(15,16)(17,18,21,22)(19,20,24,23)(27,33)(28,35)(30,36)(31,38)(1,3,6,4)(2,7,5,8)(9,10,12,14)(11,13,15,16)(17,18,21,22)(19,23,24,20)(27,33)(30,36)(34,39)(37,40)(3,4)(7,8)(11,15)(13,16)(18,22)(19,24)(25,26,29,32)(27,30,33,36)(28,31,35,38)(34,37,39,40)(1,4,6,3)(2,7,5,8)(9,11)(10,13)(12,15)(14,16)(17,19)(18,20)(21,24)(22,23)(25,27,29,33)(26,30,32,36)(28,34,35,39)(31,37,38,40)(1,5,6,2)(3,7,4,8)(9,10)(11,13)(12,14)(15,16)(17,20)(18,19)(21,23)(22,24)(25,28)(26,31)(27,34)(29,35)(30,37)(32,38)(33,39)(36,40)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.