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