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