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