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