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