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