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