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