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