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