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)(11,12,19,16)(13,17,22,23)(18,20,21,24)(25,26,31,34)(27,32,30,28)(29,37,39,33)(35,36,38,40)(2,6)(3,7)(10,15)(12,16)(17,23)(20,24)(25,27,31,30)(26,32,34,28)(29,38,39,35)(33,36,37,40)(1,3)(2,4)(5,7)(6,8)(25,28)(26,30)(27,34)(29,36)(31,32)(33,38)(35,37)(39,40) involution — undirected(1,4)(2,3)(5,8)(6,7)(9,11,14,19)(10,16,15,12)(13,21,22,18)(17,20,23,24)(25,28)(26,27)(29,36)(30,34)(31,32)(33,35)(37,38)(39,40)(9,12,14,16)(10,11,15,19)(13,20,22,24)(17,18,23,21)(25,29,31,39)(26,33,34,37)(27,35,30,38)(28,36,32,40)(9,13)(10,17)(11,18)(12,20)(14,22)(15,23)(16,24)(19,21)(25,30,31,27)(26,32,34,28)(29,38,39,35)(33,40,37,36)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.