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