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