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