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