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