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