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