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