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