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