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