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