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