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