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