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