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