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