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