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