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