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