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