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