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