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