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