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