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