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