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